Step 1: Make the Crust
In a large bowl, mix the flour and salt.
Cut in the cold butter using a pastry cutter or your fingers until the mixture resembles coarse crumbs.
Gradually add the cold water, 1 tablespoon at a time, until the dough comes together.
Shape into a disk, wrap in plastic wrap, and chill for at least 30 minutes.
Preheat your oven to 375°F (190°C).
Roll out the dough on a lightly floured surface and press it into a 9-inch pie pan.
Prick the bottom with a fork and pre-bake for 10 minutes. Let it cool.
Step 2: Prepare the Filling
In a large bowl, whisk the eggs, heavy cream, and milk until smooth.
Stir in the spinach, cheddar (or mozzarella), Parmesan (if using), nutmeg, and black pepper.
Step 3: Assemble and Bake
Pour the filling into the pre-baked crust.
Bake for 35-40 minutes or until the center is set and slightly golden on top.
Let it cool for 10 minutes before slicing.