Heat oven to 350F degrees and place oven rack one place above the middle position.
Heat a large skillet to medium and add chopped 4 slices bacon. Cook for about 3 minutes.
4 slices bacon
Add 1 chopped onion and stir together with bacon. Continue to cook on medium heat until bacon is well crisped, but not burnt, stirring occasionally. If necessary, lower heat to medium-low.
1 medium yellow onion
Once bacon is cooked and onions are starting to caramelize, add ¾ cup brown sugar, 8 ounces tomato sauce, 1 Tablespoon Worcestershire, 1 teaspoon horseradish, 2 teaspoons mustard, 1 teaspoon hot sauce, 1 teaspoon salt and ½ teaspoon pepper. Stir until brown sugar is well dissolved into other ingredients, about 3 minutes.
¾ cup brown sugar, 1 - 8 oz. can tomato sauce, 1 tbsp Worcestershire sauce, 1 tsp horseradish, 2 tsps Dijon mustard, 1 tsp hot sauce, 1 tsp salt, ½ tsp freshly ground black pepper
In a 9 x 13-inch casserole dish, add drained 28 ounces pinto, 15 ounces red, and 15 ounce black beans (rinse the black beans since they are harder to drain). Stir bacon/onion mixture into the beans.
1- 28 oz. can pinto beans, 1- 15 oz. can red beans, 1- 15 oz. can black beans
Bake 25 minutes. Lower heat to 325F degrees and cook at least another 20 minutes, up to 30. The beans may seem to lose some moisture when they come out of the oven. Just give them a quick stir and they're perfect.