Preheat your oven to 375°F. While the oven heats, place your thawed pie dough into a 9-inch pie plate, gently pressing it into the corners and sides. This gives the oven time to reach temperature while you prep the filling components.

Heat the olive oil in a large skillet over medium heat. Add the diced onion and cook for 3-4 minutes, stirring occasionally, until it becomes soft and translucent. Add the roughly chopped fresh spinach and cook for about 2 minutes, stirring frequently, until the spinach is wilted and any excess moisture has mostly evaporated. Remove from heat and let cool slightly—I find this helps prevent the eggs from scrambling when you pour them over the hot vegetables.

In a medium bowl, crack the 4 large eggs and whisk them together until well combined. Pour in the half and half and whisk until fully incorporated. Add the salt, freshly ground black pepper, and nutmeg, whisking gently until everything is evenly distributed. The nutmeg adds a subtle warmth that really complements the feta and spinach—don't skip it even though the amount seems small.

Sprinkle half of the crumbled feta cheese evenly over the bottom of the prepared pie crust, followed by half of the shredded white cheddar cheese. Spread the cooked spinach and onion mixture from Step 2 evenly over the cheese layer. This layering technique ensures every bite has a balanced mix of cheese, vegetables, and custard.

Carefully pour the egg and half and half mixture from Step 3 over the spinach and cheese layers, pouring slowly and evenly to ensure it distributes throughout the quiche. Sprinkle the remaining crumbled feta cheese and shredded white cheddar cheese over the top. Place the pie plate on a baking sheet (this catches any drips and makes it easier to remove from the oven).

Transfer the baking sheet to the preheated 375°F oven and bake for 40-45 minutes. The quiche is done when the center is just set but still slightly jiggly in the very middle—it will continue to set as it cools. The top should be lightly golden and the edges should pull slightly away from the sides of the pie plate.

Remove the quiche from the oven and let it rest on the baking sheet for at least 10 minutes before slicing. I always let mine cool a bit longer—about 15 minutes—because it holds together better and the flavors settle. Slice into wedges and serve warm or at room temperature.