- Allow the beans to defrost. Mash with a fork, or whizz a little with the blender. Don’t make them too pulpy, leave a bit of texture.
- Put the egg and breadcrumbs in a bowl and allow the bread to soak up the egg. Mix well. Add the beans.
- Grate the onions and squeeze out most of the liquid. Add to the bean mixture and mix well.
- Shape the mixture into 2–3 burgers. Put the crushed crisps on aplate and roll the burgers in them.
- Heat oil in a frying pan and cook the burgers for about 5 minutes each side. Take care that they do not burn. If they brown before the 5 minutes, just turn them and turn down the heat. They will need a total of 10 minutes in order to be heated through.
- While they are cooking, slice the other onion (for the toppings) and fry in a saucepan until caramelised (i.e. really brown). You will need to stir them frequently.
- Slice the burger bun in half, horizontally. Put the burger inside, with the onions on top and some tomato sauce and pickle to finish. Enjoy!