Preheat oven to 400 degrees F (200 degrees C). Grease a 9x13 inch casserole dish.
Place bacon in a large, deep skillet. Cook over medium high heat until evenly brown. Drain and set
In a separate skillet, melt the butter and fry onions and mushrooms until tender.
Place potatoes in bottom of prepared dish. Sprinkle with salt, garlic salt, and pepper. Top with bacon,
then onions and mushrooms.
In a large bowl, beat eggs with milk and parsley. Pour over casserole. Top with grated cheese. Cover
and refrigerate overnight.
Bake in preheated oven for 1to 1.5 hour or until set. If preparing and baking the same day, cook for 45
minutes. It must be golden brown on top. No shimmying in the middle either.