1 small chopped onion 3 eggs 1 cup sour cream or greek yogurt 8-16 ounces sliced mushrooms 1 package chopped spinach, thawed 5 tablespoons butter 2 1/2 cup grated Swiss cheese 2 pre-baked pie shells Preheat oven to 375 degrees. To thaw spinach, cook in a saucepan over medium heat. Drain spinach in mesh strainer and set aside.