A rich source of spices (especially black pepper and cardamom), Kerala has attracted traders to its ports for more than two thousand years and has welcomed Christians, Muslims, and Jews to settle its shores for almost as long (though many of the Jews left in the middle of the last century for the newly created State of Israel). There is a refreshing open-mindedness here, and it's reflected in the comfortable coexistence of these religions—so different from the strife of the north.

My father was raised here, in this lush, narrow state at India's tip, and it's still home to his sister, Kamala. I've been coming here since I was a child. This time I'm here for Onam, a ten-day harvest festival that falls during the lunar month of Chingam (August⁄September), after fruits, vegetables, and rice have been reaped from the fields.

Onam is the state's biggest holiday. People visit their families, heads of households give new clothes to younger relatives and to servants, and children decorate the ground in front of their houses with pookalams, concentric circles of fresh flowers. Celebrations take place throughout Kerala: a spectacular boat race down the Aranmula River; an elephant procession in Thrikkakara, in central Kerala; a float competition in Thiruvananthapuram (Kerala's capital, formerly called Trivandrum); folk dances; puppet shows; and an especially lighthearted pastime—swinging on swings while singing folk songs. The crowning event, though, is a family feast of Kerala's most classic, vibrant vegetarian curries, eaten on the final day.

When our car at last reaches the town of Kottayam, we turn away from the bustle of the big road and into a series of small lanes to the quiet compound where Aunty Kamala lives. As the sedan crunches down the gravel driveway, she emerges onto the front porch of her two-story whitewashed house. It's a familiar sight: my bespectacled aunty, dressed in a neat white sari, her silver hair tied into a bun, hands clasped, a smile on her face. She hugs me, her eyes glowing, and murmurs, "Welcome back, it's good to see you." I step into the house, with its cool terrazzo floors and whirling ceiling fans, and sit down to a delicious lunch of chicken simmered with fennel and potatoes, fried rice flecked with green chiles, and a tomato-red onion salad. Aunty Kamala is a gifted cook, and her food has inspired me to write two books about the little-known cuisine of this region. I'm definitely looking forward to her version of the Onam feast.

At the heart of Onam lies the ancient Hindu myth of Mahabali, a legendary Kerala king who reigned in a peaceful and prosperous time. So beloved was Mahabali that the gods grew jealous, and Lord Vishnu—one of the three major deities in the Hindu pantheon—devised a way to destroy his power. In the form of Vamanan, a poor dwarf, Vishnu appeared before Mahabali and asked to be granted as much land as he could cover in three strides. The king agreed, but as soon as he did, Vamanan assumed his divine aspect and covered the earth in one step, the heavens in the next. Humbled, Mahabali offered his head to the god for his final step, and Vishnu pushed him into the underworld. But so distraught were Mahabali's subjects that Vishnu allowed the former king to return to earth once a year to visit his people. Onam marks the period when Mahabali's spirit enters every home and is a time to rejoice in prosperous harvests, past and present. It has been an official government holiday since 1961, and Hindus tend to think of it as a secular event focused on the region's history and harvest. Not surprisingly, Christians and Muslims are likely to see it as a Hindu festival, since its origins are, after all, Hindu, and so is its signature food.

Yet it's certainly a holiday in which all Keralites participate. People of all religions enter the boat race, for instance, and Christians send one another Onam greetings in the local newspaper. Both Christians and Muslims occasionally go to restaurants during Onam to order the Hindu feast (some Hindus do, too), or cook their own Onam dinners, adding their family's favorite dishes to the vegetarian Hindu standards. There's also a wonderful custom of pakarcha ("sharing"), which involves giving food to friends and neighbors of other religions. "We exchange whatever good things we make during a festival," my aunty explains. She used to have a Syrian Christian neighbor who, at Easter, would bring over a stack of scrumptious rice-and-coconut appams, or pancakes, with a stainless-steel tiffin of chicken curry. And every Onam, Aunty would give that neighbor a container full of sweet payasam—a thick, milky pudding made with rice or noodles or, sometimes, legumes. Likewise, my cousin Syamala and her family, who live outside Kochi, give their vegetarian Onam curries to a neighboring Muslim family and in exchange receive a tidy package of pathiri, the Muslim rice-flour flat breads, during the Muslim fasting-and-feasting month of Ramadan.

It's the evening of the ninth day of the festival, and I'm in downtown Kottayam with my cousin Padma's two college-age daughters, shopping for vegetables for tomorrow. At a fluorescent-lit cubbyhole stacked with produce, Nisha and Suchu pick out slender green eggplants, green beans, an enormous cucumber, and fistfuls of fresh chiles. On the way back, we get stuck in a jam of cars, scooters, and buses; everyone is out buying last-minute groceries and gift clothes. We inch past sari shops advertising holiday sales and stores decorated with strings of white lightbulbs. People hustle along crowded sidewalks. The whole atmosphere reminds me of Christmas Eve, even though it's about 80 degrees.

We come home to an aromatic dinner of Aunty's light dosas (rice and legume crepes) served with fresh coconut chutney and a spicy vegetable-and-legume stew called sambar. Afterward we gather around the television and watch Onam programs—highlights from the parade in Thiruvananthapuram and a group of young women performing a Kerala folk dance, their bare feet moving in a circle, their long, shiny black braids woven with jasmine flowers.

The next morning I wake up to the sound of pouring rain and the warm perfume of coconut oil floating up from the kitchen. When I get downstairs, Aunty, smiling, hands me a folded sari and blouse in a delicate cream edged with gold and orange and says, "Happy Onam, Maya!" I give her a hug and ask if she'll help later in putting it on, because I'm hopeless at draping the fabric myself.

In the kitchen, my cousin Padma is sitting on a chair slicing green beans into a plate on her lap. She'll use them in her thoren, a stir-fry with mustard seeds and coconut. Along with her daughters, Padma shares this house with Aunty (both women are widowed) and is a deft and skillful cook herself. I marvel at how the two of them move in synchrony in this small room, seeming to read each other's minds, and it strikes me that the strong female bonds that are deeply part of Kerala's culture are especially evident in this kitchen.

Until the 1950s, many of Kerala's Hindus still observed the region's long-standing matrilineal system, in which property was passed down from mother to daughter. It's not uncommon even today for a married daughter to live with her mother (unlike elsewhere in India, where a woman automatically becomes a member of her husband's family). My Aunty lived and cooked with my grandmother; Padma lives and cooks with Aunty; and now I see Padma's daughters, not yet married, keeping the tradition alive as they stir curries and mix spices with Padma.

In the same compound, steps away, there's another whitewashed house, an older one with a peaked tiled roof, built by my grandfather. It's home to my cousin Mini, her husband, Mohan, and their three boys. The two households are closely intertwined, with children bouncing from one to the other and curries passed back and forth; but because cooking is part of the pleasure of Onam, today each house will make and serve its own feast.

The toasty smell of frying mustard seeds fills the air as Padma begins to cook the thoren. After she heats the seeds in hot oil, making them pop and release their flavor, she adds fresh curry leaves (not curry powder but an aromatic herb, Murraya koenigii) and whole dried red chiles. This technique, called katuku-varakkal ("mustard-seed frying"), is the first step in making many of Kerala's curries and gives the finished dish a compelling, savory fragrance.

Out in the yard, T. M. "Babu" Baburaj, the gardener, climbs one of the coconut trees and hacks down a few ripe fruits, then brings them, damp with rain, to Aunty. She splits one with the backside of a machete, then sits on a chirava—a low bench that has a serrated blade attached to one end—and uses the blade to scrape out the meat. Next, she whirs the snowy pile in a blender with water and presses the mixture through a sieve. The rich coconut milk that streams forth is a main ingredient in olan, a fragrant, liquidy curry with cucumber and curry leaves. Olan and thoren are always part of this feast, along with dhal—cooked seasoned legumes—and aviyal, a mixed-vegetable curry with a thick sauce of grated coconut and a touch of sour tamarind.

In the corner of the kitchen, a large bronze pot full of aviyal simmers under Aunty's watchful eye. After giving it a stir, she samples it, then adds a pinch more salt. "The first thing we learn in cooking," she reminds me, "is to have the right amount of salt, and the salt must be in balance with the chile and the sour." (This was one of my grandmother's main rules for making a good curry, and it's one I, too, follow when I cook Indian food at home in New York City.)

Outside, the rain has given way to afternoon sunshine, and Babu is cutting down banana leaves—the plates for our feast. Padma washes off the leaves and sets them in the sun to dry, then comes into my bedroom and pleats, tucks, and drapes my new sari around me. Meanwhile, Nisha and Suchu put bowls of curries on the dining room table. Next door at Mini's house, they're being more traditional with their seating arrangements, unrolling grass mats and spreading their banana leaves on the clean floor. Mini also lights an oil lamp and sets a small plate of food next to it as an offering to Ganesh, the beloved elephant-headed god, the bringer of good luck.

At Aunty's house, the girls and I sit down at the large wooden table. Each of our leaf plates already holds two pappadums (crisp legume wafers), a few pieces of fried banana, and a tiny sweet whole banana, set off to the left. (The fresh fruit is saved for last, but the fried bits are nice to munch on first.) Aunty and Padma move around the table, spooning out aviyal, olan, and thoren, plus a little ginger pickle, across the top half of the leaf. Aunty scoops a large paddleful of rice on the lower half—the dominant position on the leaf, since rice is mixed with every mouthful of curry—and ladles the golden cheru parippu over the right side of the rice. Then we each drizzle ghee (clarified butter) on the rice, crush a pappadum over it, and the feast begins!

Following the Indian custom of eating with the fingers of the right hand, we form plump grains of rice, crisp bits of pappadum, and earthy dhal into bites, mixing in different curries as we go, savoring the layers of coriander, cumin, and turmeric and the occasional jolt of green chile and cayenne. I'm tasting the aviyal, tart on my tongue and thick with grated coconut. Now the green-bean thoren and all its mustard seeds are crunching in my mouth. My favorite, though, is Aunty's simple olan—chile-spiked cucumbers mellowed by smooth coconut milk.

Aunty is sitting with us at the table, but continually gets up to replenish our plates with more curry, more rice. "Mathi! Mathi!" ("Enough! Enough!") I insist, and flip my leaf closed—the sign that I can't eat another thing. Everyone else seems sated, too; leaves are flipping shut all around the table. But Aunty has more for us. She goes to the kitchen and brings out little bowls of payasam, a cardamom-scented pudding of reduced milk, wheat noodles, cashews, and raisins, and full as I am, I know I can't miss this essential, delicious dessert. It's warm and velvety, and when my last spoonful disappears, I know I've truly feasted.

The contentment around our table reminds me of the story that my cousin Syamala told me: During Onam, her mother used to take food not only to her Muslim neighbors but also to the Christian family next door. One year, close to Onam, Syamala's great-uncle passed away, and the family, in mourning, did not plan a celebratory feast. The Christian neighbors knew Syamala's mother wouldn't be cooking, so, in the spirit of pakarcha, they made all the Onam dishes themselves and brought them to Syamala's family. It is generosity like this, between friends, between neighbors, between religions and cultures, that keeps the social fabric of this state woven tight and strong.