Instructions

1. The day before you plan to roast the meat, cure and tie the roast: In a small bowl, combine 2 teaspoons salt with the thyme, pepper, garlic powder, and sage. Lay the pork on a cutting board and rub it all over with the salt mixture. Starting with the wider end, roll the pork belly into a tight cylinder (ideally, the ends should overlap slightly). Using kitchen twine, tightly tie the roll crosswise every 2 inches.
2. Transfer to a rack set in a baking pan and refrigerate uncovered for at least 8 hours and up to 24 hours.
3. Preheat the oven to 350°. Using paper towels, sop up any juices that have accumulated in the baking pan and discard. Tent the pork loosely with foil. Transfer to the oven and cook for 1 hour. Lower the oven temperature to 325°, and roast 1 hour more. Reduce the temperature to 300°, remove the foil, and roast the pork until it feels tender when poked with a fork, another 1¾ to 2 hours. Remove from the oven, and let cool to room temperature.
4. Transfer the pork to a platter. Pour the fat and juices from the pan into a bowl and reserve. (Pork can be roasted a day in advance. Wrap and refrigerate, then bring to room temperature before proceeding.)
5. Prepare the pickled mushrooms and leeks: In a small saucepan, combine ¼ cup water with the vinegar, lemon juice, lemon zest, sugar, ¾ teaspoon salt, and 2 tablespoons reserved pork fat and juices; bring to a simmer. Remove from the heat, transfer to a wide bowl, and set aside.
6. Trim the mushrooms and rub clean with a wet cloth. Slice them into ½-inch-thick pieces.
7. Carefully trim the leeks, leaving the root ends attached and leaving 4 inches of green on the tops. Slice the leeks down the middle (continue to leave the root ends attached) and rinse them well under cold running water, taking care to keep them intact. Sandwich the leeks back together, and using kitchen twine, tie them into two bundles.
8. Bring a large pot of water to boil and set a bowl of ice water next to the stove. Add the leeks to the boiling water and let cook until just tender when poked with a fork, 4–6 minutes.
9. Using tongs, transfer the leeks to the ice water. When cool to the touch, drain completely. Remove the string and any wilted outer leaves, and slice the leeks into 3-inch-long pieces on the diagonal.
10. Heat a large cast-iron skillet over high heat. Season the mushrooms and leeks with some salt and pepper. Add enough pork fat to the pan to just thinly coat the bottom, 2–3 tablespoons. (If there isn’t enough pork fat, you can add canola oil as needed.) Once hot, working in batches, add the leeks in a single layer; cook, turning once, until lightly caramelized all over, about 4 minutes per side. Transfer the leeks to the bowl of pickling liquid as you work, then proceed with the remaining leeks and the mushrooms, cooking the mushrooms about 4 minutes per batch. Toss all of the vegetables in the pickling liquid to coat. Set aside at room temperature.
11. Finish the pork: Cut away the twine, then slice the pork crosswise into 1-inch-thick slabs. Heat a large cast-iron skillet over medium-high heat and add as many pieces of pork as you can fit; let cook, turning as needed, until crispy and browned on both sides, 8 minutes total. Transfer the slices to a large platter and repeat with the remaining pieces, discarding some of the excess fat from the pan if desired. Sprinkle the dill and parsley over the pork. Spoon the pickled vegetable mixture on and around the pieces and serve immediately.