Preheat the oven to 375 degrees Fahrenheit (190 degrees Celsius).

In a large skillet, cook the ground beef and diced onion over medium heat until the beef is no longer pink. Drain any excess grease.

Stir in the canned corn, cream of mushroom soup, 1/2 cup of shredded cheddar cheese, milk, sour cream, garlic powder, onion powder, salt, and pepper. Mix well to combine.

Pour the beef mixture into a 9x13-inch baking pan.

Arrange the frozen tater tots in a single layer on top of the beef mixture.

Sprinkle the remaining shredded cheddar cheese evenly over the tater tots.

Bake the casserole uncovered for 25-30 minutes, or until the cheese is bubbly and the tater tots are thoroughly cooked and golden brown.

Remove from the oven and let it cool slightly before serving.