Preheat oven to 350 degrees. Lightly coat a pie plate with cooking spray.
Heat olive oil in a large skillet over medium heat. Add onion and cook until tender, about 5 minutes. Add garlic and cook just until fragrant.
Add spinach to the pan and cook until wilted and moisture has evaporated. Remove from heat.
In a large bowl, whisk together eggs, sour cream, milk, salt and pepper. Stir in the feta cheese, mozzarella cheese, and the cooked spinach mixture until combined.
Pour into the prepared pie plate and sprinkle with the shaved Parmesan cheese and smoked paprika.
Bake for 45-50 minutes or until set and golden. Allow to rest for 5 - 10 minutes before serving.
Start checking your crustless spinach quiche during the last 5-10 minutes of baking. Every oven is different, so baking time can vary.
Not all pie plates bake the same! Metal will heat much too quickly and can cause the outer layer to burn. Ceramic will bake evenly and consistently, but glass is fine for this recipe as well.
You can place your pie plate on a rimmed baking sheet so it’s easier to transfer in and out of the oven.
To reheat the quiche, remove the dish from the refrigerator, letting it sit on the counter while you preheat the oven. Bake at 350 degrees for about 20 minutes or until warmed through. You can also reheat individual servings in the microwave or air fryer if you prefer.