Easy Beef Potpie

1/2 cup chopped onion
2 tablespoons butter
2 cups cooked beef, cut into 1/2-inch pieces
1 cup frozen peas and carrots, cooked
1 cup diced cooked potatoes
1 cup beef gravy
1/4 cup butter
1-1/2 cups flour
1 cup grated cheddar cheese
2 teaspoons baking powder
1 teaspoon salt
1/2 cup milk
   Preaheat oven to 350 degrees. In a skillet over low heat, melt 2 tablespoons butter; add onions and sauté until tender.
   Combine onions with chopped beef, cooked peas, carrots, potatoes and gravy; set aside. Melt 1/4 cup butter in bottom of an 8-inch square baking dish.
   Combine flour, cheese, baking powder, salt and milk in a mixing bowl. Stir until blended. Pour into baking dish; pour beef mixture over the batter. Do not stir. Bake the beef pie for 55 to 65 minutes or until crust is brown and filling is bubbly.