Step 1

Simmer the potato for 12–15 minutes, or until very tender but not breaking apart. Drain well and leave to air dry for a few minutes.

Step 2

In a bowl mash the rinsed beans with a potato masher and then add the potatoes and mash those too. Next add all the remaining burger ingredients, except the oil, and mix well. Shape the mixture into four large patties.

Step 3

Heat 2 tablespoons of the oil in a large frying pan (preferably non-stick). Cook the burgers over a medium heat for 3–4 minutes on each side until golden, adding a little extra oil when the burgers are turned.

Step 4

Toast the buns, in a dry frying pan or griddle on the cut side and divide between four plates. Add lettuce and tomatoes, if using. Top with the hot burgers and serve with sauces of your choice.