1 tablespoon vegetable oil, divided
2 pounds ground beef
1 tablespoon butter
1 cup button mushrooms, diced
2 onions, diced
1 (10 ½) ounce can condensed beef broth
1 (10 ½ oz) can condensed cream of mushroom soup
2 teaspoons Worcestershire sauce
3 cups water
¼ cup salted butter
1 ½ cups milk
8 ounces instant mashed potato mix
Preheat the oven to 400 degrees Fahrenheit.
Heat half of the oil over high heat in a medium saucepan. Add the beef and brown on all sides. Drain the beef and discard the fat; set the drained beef aside.
In the same pan, heat the remaining oil with the butter over medium heat. Add the mushrooms and onion and cook, stirring occasionally, until slightly browned, about 15 minutes.
Return the beef to the pan with the mushrooms and onions, and add the broth, condensed soup, and Worcestershire sauce. Stir until well combined.
Transfer the meat mixture to a greased 9x13-inch casserole dish, and spread out in an even layer.
Heat the water and butter in a saucepan. When it comes to a boil, remove from the heat and add the milk. Whisk in the instant mashed potato mix. Allow to set for a minute before mixing once more spreading in an even layer on top of the meat mixture.
Bake for 20-25 minutes, until slightly browned on top.