1) Lightly toast the pine nuts for 2-3 mins, in a frying pan, over a medium heat until golden. Remove and set to one side. 2) Put the borlotti beans and kidney beans into a large bowl and mash well. Add the pine nuts, onion, tomato paste, the breadcrumbs, thyme and egg. Season well, then mix together until thoroughly combined. 3) Shape the mixture into 4 burgers. Cover and chill in the fridge for at least 30 mins. 4) To cook fry in the oil for 3-4 mins each side until golden. Drain on kitchen paper, then serve in toasted buns with toppings of your choice.