In a skillet, cook the ground beef and chopped onion over medium heat until the beef is browned and the onion is tender. Drain any excess fat.
In a large bowl, mix the cooked beef and onion with the cream of mushroom soup, sour cream, and half of the shredded cheddar cheese. Season with salt and pepper to taste.
Spread the beef mixture evenly in a baking dish. Arrange the tater tots on top in a single layer.
Bake in the preheated oven for 30-35 minutes, until the tater tots are golden brown and crispy.
Sprinkle the remaining cheddar cheese on top and bake for an additional 5-10 minutes, until the cheese is melted and bubbly.
Let the casserole cool for a few minutes before serving.
Notes:
This casserole is perfect for a cozy family dinner. You can also add vegetables like peas or green beans for extra nutrition.