Rancho Baked Beans

3 tablespoons butter
1 cup chopped onion
1 pound ground beef
1 teaspoon seasoned salt
1/2 teaspoon Worcestershire sauce
1 tablespoon prepared mustard
1/4 cup brown sugar
1 (8 ounce) can tomato sauce
2 (1 pound) cans pork and beans
1 can pinto beans, undrained

Brown onion and ground beef in butter. Drain grease. Combine in a cast iron skillet with the remaining ingredients. Bake at 400 degrees F for 30 minutes or until bubbly.