Step 1

Arrange a rack in the middle of the oven and heat the oven to 325°F.

Step 2

Dice 1/2 medium yellow onion (abouto 1 cup). Cut 8 ounces sliced bacon crosswise into 1-inch pieces.

Step 3

Place the bacon in a large skillet over medium heat and cook, stirring occasionally, until crisp, 8 to 10 minutes. Using a slotted spoon or tongs, transfer to a paper-towel lined plate. Remove all but 1 tablespoon of the bacon fat.

Step 4

Return the skillet to medium heat. Add the onion and 1 pound lean ground beef and cook, breaking up the beef with a wooden spoon, until the beef is no longer pink, about 8 minutes. Meanwhile, rinse and drain 1 (about 15-ounce) can kidney beans and 1 (about 15-ounce) can butter beans. Open 2 (11- to 15-ounce) cans pork and beans but do not drain.

Step 5

When the beef is ready, drain off any excess liquid. Add the kidney beans, butter beans, pork and beans, and bacon to the skillet and stir to combine. Add 1/2 cup packed dark brown sugar, 1/2 cup ketchup, 1 tablespoon cider vinegar, 1 teaspoon prepared yellow mustard, and 1 teaspoon kosher salt. Stir unil combined.

Step 6

Transfer to a 9x13-inch or other 2-quart baking dish. Bake uncovered until bubbly, about 45 minutes. Taste and season with more kosher salt as needed.