Old Fashioned Roast Beef Hash

This is truly to die for. I make whole roasts just to make this because there's never any left after it is done.

Ingredients:
2 tablespoons butter
1/2 cup chopped onion
1 1/2 cups diced potatoes
3 cups cubed leftover roast beef
2 teaspoons Worcestershire sauce
1 teaspoon salt
1/2 teaspoon black pepper
1 cup milk
1/2 cup leftover gravy

In large skillet, cook onion in butter until tender crisp. Add remaining ingredients except milk and gravy. Whisk milk and gravy together until smooth. Add to skillet. (If there is no leftover gravy, just increase milk to 1 1/2 cups.) Stir all together and bring to a boil. Reduce heat and simmer, uncovered, for approximately 20 minutes or until potatoes are done. The liquid should be absorbed.