This Hamburger Potato Casserole layers sliced Yukon Gold potatoes with seasoned ground beef, peppers, onions, and a homemade cheese sauce. It’s a from-scratch casserole made without canned soup, then baked until the potatoes are tender and the top is melted and cheesy.
Prep the potatoes: Using a mandolin slicer or sharp knife, slice the potatoes into ⅛ inch even pieces. Grease a 9x13 inch baking dish and layer half of the potatoes into the dish. Preheat your oven to 350°F.
Make the steak seasoning hamburger meat: Place the ground beef into a large skillet heated over medium and sprinkle the steak seasoning over while breaking up into small pieces. When the beef is almost cooked, pour the Worcestershire sauce over and mix in. Set aside.
Sauté the vegetables for the sauce: While the beef is cooking, melt the butter in a large saucepan. Add the onion and bell pepper until starting to soften. Stir in the garlic.
Make the cheese sauce roux: Sprinkle the flour over the mixture and stir continuously until it starts to turn golden. Slowly pour in the beef broth and whisk well. Pour in the whole milk and bring to a low simmer. Stir in the thyme, salt and pepper, lower the heat and simmer for 2-3 minutes, stirring to prevent burning.
Remove the saucepan from heat and stir in 1 cup of the sharp cheddar cheese until it melts. The sauce should be thick but spoonable.
Layer the casserole: Spread half of the beef over the potato layer then pour half the sauce over the beef. Add the cup of mozzarella over the top. Follow this by layering the remaining potatoes, beef and cheese sauce over the top.
Cover the dish with foil and bake for about 55-60 minutes, until the potatoes are tender.
Remove the foil and sprinkle the remaining cheddar cheese over the top. Place back in the oven for 10-15 minutes until the cheese is melted.
Allow the casserole to set for 5-10 minutes before serving. Sprinkle fresh sliced green onion and freshly cracked black pepper over the top.
Notes
Slice the potatoes evenly: Aim for 1/8-inch slices so they bake through at the same pace. A mandolin works well, but a sharp knife is fine.
Use Yukon Gold potatoes: Their skins are thin and tender, so I leave them on. If using Russet potatoes, peel them first.
Drain the beef: Remove excess grease before layering so it does not mix into the cheese sauce.
Keep the sauce spoonable: It should be thick enough to coat the potatoes, but loose enough to spread. Add a splash of milk if it tightens too much.
Check the center: The top can look done before the potatoes are tender. A knife should slide through the center easily.
Make ahead: Assemble up to 24 hours in advance and refrigerate. Add extra covered bake time if baking from cold.
Let it rest: Resting helps the sauce settle so the casserole scoops more cleanly.