1 tablespoon butter
1 tablespoon olive oil
1 onion, sliced
1-1/2 pounds ground beef
1/4 teaspoon black pepper
1 10.5-ounce can cream of mushroom soup
1 1.4-ounce packet dry onion soup mix
2 tablespoons all-purpose flour
1/4 cup ketchup
1/2 cup water
2 tablespoons Worcestershire sauce
1 teaspoon mustard powder
2 cups frozen green beans
3 cups mashed potatoes
Preheat oven to 350 degrees Fahrenheit and grease a 9-by-13 casserole dish.
Heat butter and oil in a large frying pan over medium heat. When melted, add the onion and turn to coat in fat.
Cook onions for about 5 minutes, until they have started to soften.
Add ground beef to the frying pan, breaking it up as you do.
Cook the onion and beef together until the beef is completely browned.
While the ground beef is cooking, combine the cream of mushroom soup, dry onion soup and all-purpose flour in a large bowl. Whisk together until there are no lumps.
To the soup mixture in the bowl add ketchup, water, Worcestershire sauce and mustard powder. Whisk to combine.
Pour the soup mixture into the frying pan with the beef once the beef is browned. Add the green beans and bring to a boil.
Pour the frying pan mixture into the prepared casserole dish. Spread the mashed potatoes evenly over top.
Place the casserole into the preheated oven and bake for 20 minutes, until potatoes are golden.
Serve hot.