Brown the venison in a cast iron skillet along with the diced onion and seasonings.
While the venison is cooking, toss together potatoes and butter in a large mixing bowl.
Once the venison is browned, drain grease (if applicable) and add the meat to the mixing bowl.
Stir in sour cream, cream of mushroom soup, and one cup of cheese.
Add everything back to the skillet to bake for 55 minutes.
Add the remaining cheese to the top for the last 10 minutes in the oven.
Notes
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Dice your potatoes up small, about the size of hash browns, to ensure they cook through.
Let the casserole cool before serving. This will help the flavors to meld together and the casserole to set.
Be sure to brown the ground venison before adding it to the casserole. This will ensure the meat is cooked through and prevent the meat from being mushy.