Spray slow cooker with cooking spray. Put a layer of potatoes, then a layer of onion in bottom of cooker. Layer ALL the ground beef on top of onion. Put the remaining onion on top of beef, followed by remaining potatoes. Pour gravy or soup on top of potatoes, making sure each slice is covered with sauce. Cook on low for 8-10 Hrs or high for 4-5 Hrs or until potatoes are tender.
Tips: Be sure to follow layering instructions, as onions will be terrible if cooked on top. It is very important that potatoes be covered with soup or they will be tough. Hubby likes it soupy so I usually use two cans, but it's strictly a personal preference. Nearly any kind of cream soup works, as well beefy mushroom, french onion, ect. If there are brown bits left in the skillet, I put the liquid in the pan and scrap the bits up. Adds a lot of flavor to sauce. You can also increase the number of servings very easily in this dish. Just make sure your slow cooker is big enough to handle it. LOL
This will smell wonderful when you get home. Pair with a salad and crusty bread and you have your evening meal.