Mix everything together in a giant bowl starting with the butter and mushroom soup.
Dump it in a large resealable freezer bag.
Remove the excess air.
Seal.
Freeze.
Oven Cooking instructions:
Thaw somewhat.
Bake at 350° in a greased casserole dish for an hour.
Top it with ketchup, salsa, or hot sauce if you want.
Slow Cooker Cooking instructions:
Thaw somewhat.
Dump bag contents into your slow cooker and cook on low for 3-5 hours.
Notes
Pro tip: Because of the potatoes and cheese, this casserole tends to stick to the crockpot, so I tend to use a Slow Cooker Liner when I make this dish.If you would like to add cubed ham or ground sausage (cooked and drained) to this dish, add it (1-2 cups) and also mix in a can of evaporated milk before freezing.