1In a medium bowl, mix flour and salt. Working quickly, use your fingers to add the cubed butter to the flour mixture and break up until butter is in pea-size bits.
2Make a hole in the center of the mixture and pour in cold water. Incorporate water into the mixture until well combined and form into a ball. If dough feels too dry, add a tablespoon of water at a time until it is moist but not sticky. Wrap dough in plastic and refrigerate for 30 minutes.
3Heat olive oil over medium heat. Add the handfuls of spinach and cook until wilted. Drain in a colander and set aside.
4Pre-heat oven to 350F. In a medium bowl, beat eggs together with cream, milk, salt, and pepper. Set aside.
5On a lightly floured flat surface, roll out dough to a 12-inch circle. Gently fold the dough in half, place in a tart shell or pie pan, unfolding to fit. Lightly press the inside bottom edges of the dough against the pan’s sides to eliminate air bubbles. Roll the rolling pin across the edges of the shell to cut off the excess crust.
6To the bottom of the tart shell, add the spinach, ham, and Gruyère. Pour 3/4 of the egg mixture on top and transfer to a baking sheet. Place in oven on rack and top off with the remaining egg mixture.
7Bake for 50-60 minutes until the egg has set, and quiche is puffed and golden brown. Remove from oven and let cool slightly. Serve warm or cool and enjoy!