4 tablespoons (1/2 stick) butter or extra virgin olive oil, plus a little more for the tart
3pounds leeks, trimmed, sliced, and washed
Salt and black pepper to taste
1/2cup dry white wine or water
1/2cup chopped fresh parsley leaves
4 eggs
1/2cup heavy cream, half-and-half, or milk
1cup grated Gruyère, Cantal, Cheddar, or other firm but not dry cheese
1/4cup freshly grated Parmesan
Instructions
Preheat the oven to 400°F. Tear off a piece of foil twice as large as the crust. Fold it in half and smear it with butter or oil; lay the greased side onto the crust. Weight the foil with a pile of dried beans or rice (these can be reused for this same purpose), pie weights, or a tight-fitting skillet or saucepan—anything that will sit flat on the surface. Bake for 12 minutes, then remove the foil and continue to bake at 350°F until the crust is a beautiful shade of brown, just a few minutes more. Remove and let cool on a rack while you prepare the filling.
Meanwhile, put the 4 tablespoons butter in a large nonstick skillet with a lid over medium heat. Two minutes later, add the leeks, along with a large pinch of salt and some pepper. Cook, stirring occasionally, until they begin to soften, about 5 minutes. Add the liquid and bring to a boil; cover and adjust the heat so the mixture simmers. Cook, stirring occasionally, until the leeks are very soft, at least 20 minutes. If a great deal of liquid remains, remove the lid and cook over medium heat until you have a moist but not soupy mass. Taste and adjust the seasoning, then cool slightly. Reserve 1 1/2 cups for the tart and refrigerate any extras for another use (they’re great for sandwiches, to toss with pasta, or stir into scrambled eggs).
Combine the leeks with the remaining ingredients and pile this mixture into the prebaked shell. Bake for 30 to 40 minutes, or until almost firm and lightly browned on top; reduce the oven heat if the shell’s edges are darkening too quickly. Cool for at least 10 minutes before slicing and serving.