Family Beef Salisbury Steak

Preheat oven to 350 degrees F (175 degrees C).

Prepare a large casserole dish with cooking spray.

Lightly mix ground beef, 1/2 cup onion, bread crumbs, 3 tablespoons beef broth, milk, and 1/4 teaspoon black pepper together in a bowl; divide into 5 portions and shape into patties.

Season flour with salt and pepper in a wide, shallow dish.

Gently lay patties into the flour to lightly coat.

Heat vegetable oil in a 10-inch skillet over medium-high heat.

Fry patties in hot oil until browned completely, 3 to 5 minutes per side.

Remove patties to a plate lined with paper towel to drain excess grease.

Stir remaining beef broth, cream of mushroom soup, salt, and 1/4 teaspoon black pepper together in a bowl until smooth.

Arrange drained patties into the prepared casserole dish.

Spread onion slices atop the patties and pour the soup mixture over the patties to cover completely.

Bake in preheated oven until no longer pink in the center, 45 minutes to 1 hour.

An instant-read thermometer inserted into the center should read at least 160 degrees F (70 degrees C).