Preheat your oven to 400°F. Generously butter the bottom and sides of a 9-inch ceramic or glass pie plate.
Place the spinach in a microwave-safe bowl. Cover and microwave until thawed, about 4 minutes. Allow to slightly cool. Place the spinach in a colander and press on it repeatedly with the back of a large spoon to drain as much water as possible.
Whisk the eggs, sour cream, kosher salt, black pepper, garlic powder, onion powder, and dried thyme in a large bowl.
Using a spatula, stir in the spinach and parmesan.
Pour the mixture into the prepared pie plate. Bake until the quiche is puffed, its edges are browned, and its center appears set, and a toothpick inserted in its center comes out clean, 25-30 minutes.
Cool the quiche for 15 minutes in the pan on a cooling rack before slicing and serving.
Video
Notes
The only somewhat challenging part of this recipe is ensuring that the defrosted spinach is as dry as possible. You'll need to squeeze out as much water as you possibly can to ensure a firm, non-watery quiche.This quiche keeps beautifully in the fridge, in an airtight container, for up to 4 days. You can also slice it into individual slices and freeze the slices.