Place ½ lb uncooked bacon, chopped in a large skillet. Cook until crisp. Set aside. Pour the bacon grease into a small dish and reserve for another use.
Place 1 lb ground beef and 1 large yellow onion (diced) in the skillet. Cook until the beef is cooked through and the onion is soft, about 6–8 minutes. Break up the ground beef with the end of a wooden spoon as it cooks.
Add 1 (15 oz) can red kidney beans (drained), 1 (15 oz) can butter beans (drained), 1 (15 oz) can pork and beans, ¼ cup water, ½ cup brown sugar, ½ cup granulated sugar, 1 tablespoon white vinegar, 1 teaspoon dry mustard powder, ½ cup ketchup, and 1 teaspoon salt to the skillet and stir to combine.
Transfer the mixture to a 13x9 inch baking dish (or another 3 quart baking dish). Cover the dish with foil.
Bake for 30 minutes, or until bubbly. Serve immediately.
Notes
You can make the baked beans in a crockpot instead of the oven. To use a crockpot, cook the bacon, beef, and onions on the stove as directed. Transfer the mixture to a crockpot and top with the remaining ingredients. Stir and place the lid on top. Cook for 1.5–2 hours on high or 3–4 hours on low. Don't have dried mustard? Replace it with 2 teaspoons yellow or dijon mustard.