Add olive oil to a large oven-proof skillet (or large frying pan) over medium-high heat. Add the ground beef, breaking it up with a spatula or large spoon.
1 tbsp olive oil, 1 lb ground beef
Add the sliced onion and mushrooms and cook alongside the ground beef, about 2-3 minutes until slightly softened and the beef starts to get brown. Add the minced garlic and cook for 30 seconds until fragrant. Season the mixture with salt, ground black pepper, and Italian herbs.
1 yellow onion, 8 oz white button mushrooms, 2 garlic cloves, 1/2 tsp Italian herbs, 1 tsp salt, 1/2 tsp ground black pepper
Sprinkle the cornstarch over the mixture and stir to combine. Cook until the mixture thickens, about 1 minute.
2 tbsp cornstarch, 3/4 cup beef stock
Stir in the beef stock and cook the sauce for 2-3 minutes until it thickens. Remove the pan or skillet from the heat. Add the heavy cream and stir to combine. Season to taste with salt and pepper.
1/2 cup heavy cream
Place the frozen tater tots on top of the thickened beef and mushroom mixture. Sprinkle over the parmesan cheese and bake it in the oven for 20 minutes until the tater tots are fully cooked and the cheese is melted. Switch on the broiler or grill for the last 5 minutes if the tater tots don't have enough color yet. You want them to be nice and crispy!
2 cups mini hashbrowns, 1/2 cup grated parmesan
Remove the tater tot casserole from the oven and let it sit for 10 minutes before serving to slightly cool it down. Garnish with fresh parsley (optional) and serve.
1 tbsp fresh parsley
Video
Notes
Adjust consistency: If the sauce is too thick, you can thin it out with a little bit of extra beef broth.Storage: Leftover meat casserole can be stored in an airtight container in the refrigerator for up to 3 days. Reheat gently over low heat until warmed through. I don't recommend freezing it as the tater tots will be soggy and the creamy sauce can separate when thawing.