- Preheat the oven to 200°C/400°F
- Split the buns down the middle and brush with butter on the top and bottom of the bun.
- Lay the bottom half of the bun on a flat lined baking tray and top with cooked onions, cooked hot dogs and grated cheeses.
- Lay another piece of paper over the top and flatten with a heavy tray of similar size.
- Bake for 15/20 mins until the cheese has melted.