Three Bean Casserole

INGREDIENTS
½   cup chopped white onion
1    pound lean ground beef (under 10% fat)
1    can (15 ounces) red kidney beans, rinsed, drained
1    can (15 ounces) cannellini beans, rinsed, drained
1    can (15 ounces) black beans, rinsed, drained
1    can (8 ounces) tomato sauce
¼   cup chicken or beef broth
1    tablespoon Dijon style mustard or equivalent
¼   cup packed brown sugar
2    tablespoons white vinegar

METHOD

Preheat the oven to 325 F. In a large skillet overt medium heat, add the onion and hamburger and cook the ground beef until it is no ,longer pink, breaking it up with a wooden spatula as it cooks. Add the beans to the skillet off the heat.

 n a small bowl, combine the tomato sauce, broth, mustard, brown sugar and vinegar, mixing well. Pour into the skillet and stir to combine. Pour the mixture into an 8 by 8 or slightly larger baking dish, cover with aluminum foil or other cover and bake for 20 minutes. Remove and cool slightly before serving.