1Place potatoes in a 5 qt. slow cooker.
In a large bowl, combine beef, pork, Shake 'N' Bake,beef onion soup mix, jarred mushrooms and egg.
2In a small bowl, stir together 1/2 cup Cheddar soup and milk, and add to meat mixture.
Using a wooden spoon or clean hands, mix thoroughly and form into a loaf.
Place in slow cooker on top of potatoes, making sure meatloaf does not touch the sides of the slow cooker.
3Stir together remaining Cheddar soup and mushroom soup. Pour over meatloaf. Top with onion and fresh mushrooms.
Cover and cook on HIGH for 1 hour. Set to LOW and cook for 5-6 hours longer