Roll out the dough 1/8 inch thick and fit into a buttered 9-inch quiche, tart, or pie pan. Refrigerate while you prepare the filling.
Melt in a medium skillet over medium heat:
2 tablespoons unsalted butter
Add:
2 pounds leeks trimmed to white and tender green parts only, split lengthwise, cleaned thoroughly, and cut into 1/4-inch-thick slices
1/2 teaspoon salt
Ground black pepper to taste
Cover and cook until the leeks are very soft, with little color, stirring occassionally and reducing the heat as they cook, about 30 minutes.
After about 15 minutes of cooking time, set a rack in the lowest position in the oven. Preheat the oven to 400┬░F.
In a bowl, beat together until well combined:
2 large eggs
1/2 cup heavy cream, half-and-half, or light cream
1/4 teaspoon freshly grated nutmeg or ground nutmeg
Salt and ground black pepper to taste
Remove the pastry shell from the refrigerator. When the leeks are done, add to the custard and transfer to the prepared pastry shell. Bake until golden and the custard is set, 20 to 30 minutes. Let rest for 10 minutes to settle, then cut into wedges and serve.