SERVES 4 TO 6 8 medium leeks (see Note above) white and light green parts only 2 tablespoons extra-virgin olive oil 2 tablespoons unsalted butter 6 sprigs fresh thyme 1 cup homemade or low-sodium canned chicken stock Kosher salt and freshly ground black pepper 2 teaspoons grated lemon zest (from 1 lemon) 2 teaspoons lemon juice Adjust an oven rack to the center position and preheat the oven to 375°F Split the leeks lengthwise in half, leaving the root end attached, and discard any tough outer layers Rinse under cold running water and pat dry with paper towels Heat the olive oil in a 12-inch heavy-bottomed skillet over medium-high heat until shimmering Add half of the leeks cut side down and cook, without moving them, until well browned on the cut side, about minutes Transfer cut side up to a 13-by-9-inch baking dish Sear the remaining leeks and add to the baking dish Dot the top of leeks with the butter, scatter the thyme over the top, and pour the chicken stock over the leeks Cover tightly with foil, place in the oven, and cook until the leeks are completely tender, about 30 minutes; remove the foil for the last 10 minutes of braising Remove from the oven and allow to cool for 5 minutes Discard the thyme stems, season to taste with salt and pepper, and transfer the leeks to a serving platter Stir the lemon zest and juice into the pan juices and pour on top of the leeks Serve immediately ... 13-by-9-inch baking dish Sear the remaining leeks and add to the baking dish Dot the top of leeks with the butter, scatter the thyme over the top, and pour the chicken stock over the leeks Cover tightly with foil, place in the oven, and cook until... Cover tightly with foil, place in the oven, and cook until the leeks are completely tender, about 30 minutes; remove the foil for the last 10 minutes of braising Remove from the oven and allow to cool for 5 minutes Discard the. .. Heat the olive oil in a 12-inch heavy-bottomed skillet over medium-high heat until shimmering Add half of the leeks cut side down and cook, without moving them, until well browned on the cut