Made this for Easter, and EVERYONE said it was the best quiche they had ever had. Got it off of allrecipes, and tweaked it. I use the no roll pie crust from this web site, leave it unbaked, and add the ingredients.
In a large dutch oven or pot, melt butter over medium heat. Saute garlic and onion in butter until lightly transparent. Add the mushrooms, and saute until they are fragrant. Add the spinach, and saute until it reduces down (about 4 minutes). Remove and reserve most of the liquid from the pan. Stir in all the italian cheese and all but 1/2 cup of the cheddar. Season with salt and pepper (make sure to taste at this point, as this is the only time you will be able to adjust the salt and pepper). Spoon mixture into pie crust.
In a medium bowl, whisk together eggs and milk. Pour into the pastry shell, allowing egg mixture to thoroughly combine with spinach mixture. Add in the set aside liquid if it seems too dry, and mix thouroghly.
Bake in preheated oven for 15 minutes. Sprinkle top with remaining Cheddar cheese, and bake an additional 35 to 40 minutes, until set in center. Allow to stand 10 minutes before serving.