- Preheat the oven to 180 °C (350 °F).
- In a skillet, brown the onion in the butter. Set aside.
- In a bowl, crush the beans with a potato masher. Stir in the onions and the remaining ingredients except for the ketchup. Season with salt and pepper.
- Oil medium-sized muffin cups. Spoon the meat mixture into the pans. Cover the meat with the ketchup and bake in the lowest position of the oven until the meat is cooked through, about 40 minutes (time varies depending on the size of the pans).