1. Prepare Oven and Dish:

• Preheat your oven to 375°F (190°C).
• Grease a 9×13 inch casserole dish.

2. Cook the Ground Beef and Onion:

• In a large skillet over medium-high heat, cook the ground beef, breaking it apart with a spoon, until mostly browned.
• Add the diced onion to the skillet and continue cooking until the beef is fully browned and the onion has softened, about 5-7 minutes total.
• Drain off any excess fat from the skillet very well.
• Season the beef and onion mixture with salt, pepper, and any optional seasonings like garlic powder or paprika, to your taste. Stir well.

3. Combine with Cream Sauce:

• Stir the can of cream of mushroom soup and the sour cream directly into the skillet with the cooked beef and onion mixture.
• Mix well until everything is combined and creamy. Cook for another 2-3 minutes, stirring, until the mixture is heated through.

4. Layer the Casserole Base:

• Spread the creamy beef mixture evenly across the bottom of the prepared greased casserole dish.  

5. Add First Cheese Layer:

• Sprinkle 1 cup of the shredded cheddar cheese evenly over the beef mixture.

6. Add Tater Tot Layer:

• Arrange the frozen tater tots in a single, even layer on top of the cheese. Pack them in closely to cover the surface.  

7. Initial Bake:

• Place the casserole dish in the preheated oven.
• Bake uncovered for 25-30 minutes. The tater tots should be starting to turn golden brown and crispy.

8. Add Final Cheese Layer and Finish Baking:

• Carefully remove the casserole from the oven.
• Top evenly with the remaining 1 cup of shredded cheddar cheese.
• Return the casserole to the oven and bake for an additional 5 minutes, or until the cheese is completely melted and bubbly.

9. Rest and Serve:

• Let the Tater Tot Casserole cool for about 5-10 minutes before serving. This allows the creamy base to set slightly, making it easier to scoop.
• Serve hot.