Brown the ground beef and onions on a skillet while making the mashed potatoes as you normally would.
In a slow cooker mix the chicken soup and sour cream. Mix in the mashed potatoes, stir. Add the ground beef and onions, stir. Add the melted butter, stir and let sit in the slow cooker for about 15 minutes. Once hot, add the grated cheese and stir. You can add as much as you like. Let melt and put the slow cooker on low. Enjoy.