Oven Prep: Heat the oven to 350 F and lightly grease a 2-quart baking dish.
Cook the Beef: Heat 1 tablespoon of oil or drippings in a large skillet or sauté pan over medium-high heat. Add the beef, break it up into small pieces, and cook undisturbed for 4 minutes. Continue cooking and stirring for 4 to 5 minutes or until the beef is no longer pink. Remove the beef to a plate and set aside.
Sauté the Vegetables: In the same pan, heat the remaining oil or drippings over medium heat. Add the onions, carrot, celery, and mushrooms and sauté until the onions are translucent. Stir the flour into the vegetables and cook, stirring, for 2 minutes. Add the beef back to the pan and stir to blend.
Simmer the Filling and Assemble the Casserole: Add the beef broth, Worcestershire sauce, thyme, and pepper. Bring to a simmer, then reduce the heat to low, cover the pan, and simmer for 10 minutes or until the vegetables are tender. Add more broth if the mixture is too thick. Taste and add salt, as needed. Turn the ground beef mixture into the prepared baking dish.
Stir the cheese into the hot mashed potatoes and spoon them over the top of the casserole. Spread the potatoes to cover the filling.
Bake: Bake the casserole for 25 minutes or until the filling is bubbling and the topping is lightly browned. Broil for a minute or two to brown the topping more.
Serve: Serve with a garnish of parsley if desired. Enjoy!
Instructions
Cold mashed potatoes? Warm the potatoes in the microwave to soften them enough to spread over the meat filling.