To make spinach quiche, combine spinach, mushrooms, onion, garlic and cheese with eggs and milk, and bake in a 9-inch pie crust. This recipe requires 20 minutes of preparation time and 50 to 55 minutes of baking time.
Preheat the oven to 375 degrees Fahrenheit. Melt 1/2 cup butter in a medium skillet. Saute 1 small chopped onion and 3 cloves chopped garlic until they begin to brown. Add 10 ounces chopped frozen spinach, thawed and drained, 4 1/2 ounces drained canned sliced mushrooms, 6 ounces herb and garlic feta cheese and 4 ounces shredded cheddar cheese. Stir to combine, and season with salt and pepper. Transfer the mixture to a 9-inch pie crust.
Beat 4 eggs and 1 cup milk in a medium bowl, and season with salt and pepper. Pour the egg mixture over the spinach, mushrooms and cheeses in the pie crust. Bake for 15 minutes. Remove the quiche from the oven, and top with 4 ounces shredded cheddar cheese. Return the quiche to the oven, and bake for an additional 35 to 40 minutes until the center of the quiche is fully set. Remove it from the oven, and allow it to cool for 10 minutes before serving.