Make the crust: In a bowl, combine flour and salt. Cut in the cold butter until the mixture resembles coarse crumbs. Gradually add cold water until the dough comes together. Chill for 30 minutes.

1. Roll out the dough: Roll the chilled dough into a 12-inch circle, press it into a 9-inch pie dish, and trim excess dough. Prick the bottom with a fork.
2. Blind bake the crust: Preheat oven to 375°F (190°C). Line the crust with parchment and fill with pie weights. Bake for 10-12 minutes, then remove weights and bake for another 5-7 minutes until golden. Set aside to cool.
3. Prepare the filling: Heat olive oil or butter in a skillet. Sauté onion for 3-4 minutes, then add garlic for another minute. Add spinach and cook until any excess moisture evaporates. Let cool.
4. Make the egg mixture: Whisk eggs, cream (or milk), cheddar cheese, salt, pepper, and nutmeg in a bowl.
5. Assemble the quiche: Spread the spinach mixture over the baked crust. Pour the egg mixture over it, ensuring even distribution. Top with Parmesan if desired.
6. Bake the quiche: Reduce oven to 350°F (175°C) and bake for 30-35 minutes, until set and golden. A knife inserted into the center should come out clean.
7. Cool and serve: Let the quiche cool for 10-15 minutes before slicing and serving. It can be served warm or at room temperature.