Prepare the Crust

• Combine the flour and a pinch of salt in a food processor. Add the cold, diced butter and pulse until the mixture resembles coarse crumbs.
• Gradually add ice water, one tablespoon at a time, pulsing until the dough just comes together.
• Form the dough into a disk, wrap it in plastic wrap, and refrigerate for at least 30 minutes.
• On a floured surface, roll out the chilled dough to fit a 9-inch tart pan or pie dish. Press it into the pan and trim the edges. Prick the bottom with a fork and refrigerate for 15 minutes.
• Preheat the oven to 375°F (190°C). Line the crust with parchment paper, fill it with pie weights or dried beans, and bake for 15 minutes. Remove the weights and parchment, then bake for another 5 minutes. Set aside to cool.

Sauté the Spinach

• Heat olive oil in a large skillet over medium heat. Add the chopped shallots and cook for 2-3 minutes until softened.
• Add the spinach and sauté until wilted, about 2 minutes. Remove from heat and let cool slightly.

Prepare the Filling

• In a mixing bowl, whisk together the eggs, heavy cream, milk, salt, black pepper, and nutmeg.
• Stir in the Gruyère cheese, Parmesan cheese, and the sautéed spinach and shallots.

Assemble and Bake

• Pour the filling into the pre-baked crust, spreading it evenly.
• Bake the quiche at 375°F (190°C) for 35-40 minutes, or until the filling is set and the top is lightly golden.
• Let the quiche cool for 10 minutes before slicing.