01 - Set the oven to 375°F to prepare for baking.
02 - Roll out the pastry and fit it into a 9-inch tart or pie pan. Trim any excess dough and prick the base evenly with a fork.
03 - Line the shell with parchment paper and fill with baking weights or dried beans. Blind bake for 10 minutes, then remove the weights and paper and bake for an additional 5 minutes.
04 - Whisk together eggs, heavy cream, whole milk, salt, black pepper, and nutmeg until smooth and fully combined.
05 - Evenly distribute grated cheese, chopped spinach, sautéed onions or leeks, and bacon or ham (if using) over the pre-baked pastry shell.
06 - Pour the egg and cream mixture over the layered fillings, ensuring even coverage.
07 - Bake the assembled tart for 30 to 35 minutes until the filling is set and the surface is golden brown.
08 - Allow the quiche to cool for 10 minutes before slicing to serve.