Preheat oven to 350℉.
Slice 1 pound lean ground beef into small pieces.
Put the bacon pieces, 1 pound lean ground beef, and 1 medium onion in a large skillet. Cook over medium heat, stirring occasionally, until the meat is browned and the onions are translucent. Drain any excess grease.
Add the 16 ounce can kidney beans, 16 ounce can butter beans, and 15 ounce can pork and beans.
Stir in the ½ cup brown sugar, ½ cup granulated sugar, 1 Tablespoon vinegar, ½ teaspoon mustard powder, and ½ cup ketchup.
Transfer to a casserole if using. Otherwise, you can leave the mixture in the skillet if it is oven safe. Bake uncovered for 40 minutes.
Stir and adjust the seasoning to taste.
