Gather the ingredients and preheat the oven to 375 F.
Cook steak and cut it into pieces.
Grease a 2-quart baking dish; arrange the cubed steak in the baking dish along with the potatoes, carrots, and onion.
Combine the soups in a saucepan with the butter. Place the pan over medium heat and heat until simmering. Stir to blend and pour over the steak and vegetables.
Cover the casserole with foil and bake for about 1 hour. Uncover and pierce the potatoes with a fork to test for doneness.
