Recipe Method

1. In a large pan, melt the butter and oil over a medium heat.
2. Add the onions and stir well.
3. Cook the onions for 1 hour or until they are soft, golden and caramelised. Stir them occasionally while they cook and lower the heat if they’re browning too fast. Just before they are done, add the vinegar and stir well.
4. While the onions cook, make the sauce by combining the mayonnaise, mustard, parsley and lemon juice together in a bowl.
5. Transfer the onions into a bowl and set aside.
6. Place the sausages into the onion pan and cook them over a medium heat until the skins crisp and brown. 
7. Smear the mayo mix onto the inside of the hotdog buns.
8. Place the sausages in the buns.
9. Top them with caramelised onions and sprinkle cheese over the top.