1 Preheat oven to 400 degrees F (200 degrees C). Grease a 9x13 inch casserole dish.
2 Place bacon in a large, deep skillet. Cook over medium high heat until evenly brown. Drain and set aside. In a separate skillet, melt the butter and fry onions and mushrooms until tender.
3 Place potatoes in bottom of prepared dish. Sprinkle with salt, garlic salt, and pepper. Top with bacon, then onions and mushrooms.
4 In a large bowl, beat eggs with milk and parsley. Pour over casserole. Top with grated cheese. Cover and refrigerate overnight.
5 Bake in preheated oven for 1 hour or until set. If preparing and baking the same day, cook for 45 minutes.