Make the crust: In a food processor, pulse flour, salt, and butter until crumbly. Add cold water gradually and pulse just until dough forms. Do not overmix.
Chill dough: Form dough into a disk, wrap, and refrigerate 30 minutes.
Prepare filling: Sauté onions in butter and olive oil over medium heat for about 5 minutes until soft. Add garlic and spinach, cook until wilted. Transfer to a sieve and squeeze out excess liquid. Cool slightly.
Mix custard: Whisk eggs, cream, salt, pepper, and nutmeg.
Shape crust: Roll the dough to about ⅛-inch (3 mm) thickness and gently fit it into a 9-inch (23–24 cm) tart or pie pan. Press into the corners, trim excess dough, and prick the base with a fork. Freeze for 20–30 minutes before baking.
Blind bake: Heat oven to 350°F (175°C). Line the crust with parchment and fill with weights or beans (read notes). Bake for 15 minutes, remove weights, then bake 5–10 minutes more until crust looks dry and lightly golden.
Fill quiche: Spread spinach mixture over crust. Sprinkle Gruyère and blue cheese evenly. Pour custard over filling.
Bake: Bake 30–35 minutes until edges are golden and the center is just slightly wobbly.
Rest & serve: Cool 10–15 minutes before slicing for clean pieces.
Video
Notes
Water in the crust: Add the cold water gradually, 1 tablespoon at a time, pulsing just until the dough starts to come together when pressed between your fingers. The dough should hold together but not feel sticky. You may not need all the water.
Do not over-process the dough: Mix the dough just until it comes together. Over-processing or over-kneading develops too much gluten and warms the butter, which results in a tough, dense crust instead of a tender, flaky one. Small visible butter pieces in the dough are perfectly fine,they help create a flaky texture when baked.
Spinach: After cooking, make sure to drain and squeeze out as much liquid as possible from the spinach. Excess moisture can make the quiche watery and prevent it from setting properly.
Cheese choice: Gruyère gives a classic nutty flavor and melts beautifully, but you can substitute with Emmental, Swiss, mozzarella, cheddar, or feta. Blue cheese adds depth, but you can reduce or omit it if you prefer a milder taste.
Substitutions: You can replace heavy cream with half-and-half or use a mix of milk and cream for a lighter quiche. Frozen spinach can also be used, just thaw completely and squeeze very well before adding.
Other mix-ins: This quiche works well with additions like sautéed mushrooms, cooked bacon, ham, caramelized onions, leeks, sun-dried tomatoes, or roasted peppers. Keep total mix-ins moderate so the custard sets properly.
Blind baking: Blind baking helps keep the crust crisp. Bake the crust with weights until the edges are set, then remove the weights and bake again until the base looks dry and lightly golden before adding the filling.
Storage:
Store leftover quiche covered in the refrigerator for up to 4 days. Reheat slices in the oven at 325°F (160°C) for 10–15 minutes or until warmed through to keep the crust crisp.
Quiche can also be frozen for up to 2 months. Cool completely, wrap tightly, and freeze whole or in slices. Thaw overnight in the refrigerator and reheat in the oven before serving.