Barbecue sauce adds a smoky dimension to burgers. We love the peppery version ladled onto the "hickory burger" at the Apple Pan, a 62-year-old lunch counter in Los Angeles.

Sweet pepper relish is typically a mix of sweet peppers, vinegar, and spices. Our favorite version is Howard's, made in Massachusetts.

Spiked Ketchup A pinch of curry powder or smoked paprika adds intrigue to sweet ketchup. The Los Angeles restaurant Umami Burger adds anchovy, truffle salt, oyster sauce, and soy sauce to its house ketchup.

Aioli This garlic-spiked, lemony mayonnaise brightens the flavor of a burger and produces a creamy texture.

Thousand Island Dressing The classic blend of mayonnaise, pickle relish, and chili sauce goes beautifully with the flavor of charred beef.

Nut Burger Sauce One of our favorite discoveries is this weirdly perfect sauce, invented at Matt's Place Drive-In in Butte, Montana: a mixture of Azar's Fancy Nut ice cream sundae topping and Miracle Whip.

Mustard Our choice is French's Classic yellow mustard, whose bite is a natural companion to ketchup and beef.

Flavored Mayonnaise Blend fresh or dried herbs into store-bought mayo. For a spicy spread, puree one canned chipotle, one tablespoon of the adobo sauce it's
packed in, and one cup of mayo.

Chili When we make beef chili, we always freeze leftovers so that we'll have a spicy, supremely satisfying topping for our burgers.