Add 3 tablespoons of the butter, onions, and ground beef to an oven-proof skillet.
Cooking, stirring often, until meat is cooked through and onions are tender.
Sprinkle with onion soup mix.
Stir in cream of mushroom soup.
Stir in ½ cup water.
Simmer for a few minutes. Stir often.
Cover the top with mashed potatoes.
Dot the mashed potatoes with remaining butter and add black pepper to taste.
Add the skillet to the oven and bake for 15 to 20 minutes.
Remove from oven and top with chopped green onion.
Let rest for 5 minutes before serving.
Notes
Storage:RefrigerateLet the casserole cool down a bit, then transfer leftovers to an airtight container or cover with plastic wrap. They'll last for five days in the refrigerator.FreezeFollow the steps for refrigeration, but make sure to use a freezer-safe container or tightly-covered disposable foil casserole dish.Then, freeze for up to two months. Let the leftovers thaw in the fridge before reheating.ReheatingThe best way to quickly reheat Salisbury steak casserole is right in the microwave! I like to do so in one-minute increments, stirring in between, so everything heats evenly.Tips
This makes 8 servings or 6 very hearty servings.
Make sure your skillet is oven-proof like this classic cast iron one. If it has plastic handles, it's not safe to go in the oven—they'll melt!
Don't have an oven-proof skillet? Simply transfer the cooked meat to a greased casserole dish. Then, finish assembling and bake!
Lean ground beef (90/10 or better) is best for Salisbury steak casserole. If you use a fattier mix, drain off the grease before adding the water and soup.
If you've made the casserole ahead of time, you can bake it straight from the freezer. However, it'll take a little longer. I recommend keeping it covered with foil for a half hour in the oven. Then, remove the foil and cook until everything is hot throughout.