Preheat Oven: Start by setting your oven to 350°F (175°C). This initial step ensures that your casserole bakes evenly and thoroughly for that perfect golden finish.

Sauté Beef: In a skillet, cook 1 lb of lean ground beef and ½ cup chopped onion over medium heat until browned—about 8-10 minutes. Don’t forget to drain any excess fat!

Mix Sauce: Stir together a 10.5-ounce can of condensed cream of mushroom soup with ¾ cup milk until it's creamy and well combined.

Layer Potatoes: Grease a baking dish and layer half of your 3 cups of sliced peeled potatoes at the bottom.

Combine Beef: Spread half of the beef mixture over the potato layer. Season with salt and pepper, then sprinkle half of 1 cup shredded cheese over the top.

Repeat Layers: Add the remaining sliced potatoes, followed by the rest of the beef mixture. Finish with a layer of cheese on top.

Cover and Bake: Cover your casserole with foil and bake for 60 minutes.

Final Baking: After 60 minutes, remove the foil and bake for another 20 minutes, until the potatoes are tender and the cheese is bubbly.