In a skillet over medium-high heat, brown the ground beef and onion until the beef is fully cooked and onion is soft.
Mix cooked beef, cream of mushroom soup, sour cream, and cheese in a mixing bowl.
Spread the mixture into a baking dish and top with tater tots.
Bake for 30-40 minutes or until tater tots are golden and crispy.
Notes
Store your leftover tater tot casserole in an airtight container for up to 3 days in the fridge, or freeze for up to 3 months. Reheat thoroughly before serving.