Preheat the oven to 375°F. Gently press a pie crust into a 9-inch pie plate. Trim any excess edges and set aside.
9 inch pie dough
In a large skillet over medium high heat, add the olive oil. Once heated, add the chopped onion and cook for 3-4 minutes until they soften and turn translucent. Add the chopped spinach and cook for another 2 minutes, stirring occasionally, until wilted. Remove the pan from the heat and set aside to cool slightly.
In a medium mixing bowl, whisk together the eggs, half & half, salt, pepper, and nutmeg. Make sure the mixture is smooth and evenly combined.
4 large eggs, 1 cup half & half, 1/2 teaspoon salt, 1/4 teaspoon black pepper, 1/4 teaspoon nutmeg
Sprinkle half of the feta cheese and a small portion of the shredded cheddar evenly over the bottom of the pie crust. Evenly spoon the spinach & onion mixture over the top.
3/4 cup crumbled feta cheese, 1/2 cup shredded white cheddar cheese
Pour the egg mixture over the spinach & onion layer, letting it settle throughout. Sprinkle the remaining feta cheese and the rest of the shredded cheddar on top.
Place the pie on a baking sheet to catch any spills and transfer it to the oven. Bake for 40-45 minutes or until the center is set and lightly golden. A knife or toothpick inserted in the middle should comes out clean.
Remove the quiche from the oven and let it rest for about 10 minutes before slicing. This helps it firm up and makes it easier to cut.
Slice into wedges and serve warm, or at room temperature.