Salisbury Steak Casserole

8 Preheat the oven to 375℉
0 Add 3 tablespoons of the butter, onions, and ground beef to an oven-proof skillet.
1 Cooking, stirring often, until meat is cooked through and onions are tender.
2 Sprinkle with onion soup mix.
4 Stir in cream of mushroom soup.
3 Stir in 1/2 cup water.
5 Simmer for a few minutes. Stir often.
6 Cover the top with mashed potatoes.
7 Dot the mashed potatoes with remaining butter and add black pepper to taste.
9 Add the skillet to the oven and bake for 15 to 20 minutes.
10 Remove from oven and top with chopped green onion.
11 Let rest for 5 minutes before serving.