Preheat Oven
Preheat oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish.
Make Hamburger Steaks
In a bowl, gently mix ground beef, diced onion, salt, and pepper. Form into 5–6 evenly sized patties.
Layer Potatoes
Arrange sliced potatoes evenly in the bottom of the baking dish. Season lightly with salt and pepper.
Add Patties
Place hamburger patties on top of the potato layer.
Prepare Sauce
Whisk cream of mushroom soup and milk until smooth. Pour evenly over the patties and potatoes.
Add Butter & Bake
Dot butter over the top. Cover tightly with foil and bake for 50 minutes.
Finish Baking
Remove foil and bake an additional 10–15 minutes until potatoes are tender and meat is fully cooked.
Rest & Serve
Let rest 10 minutes before serving.