1. Peel the sweet potato and white potato and chop into even small chunks. Bring a pan of water to the boil and cook the potatoes for 8-10 minutes or until tender. Drain well and mash. Leave to one side.
2. In a bowl mash the beans and combine with the mashed potato mixture.
3. Pre-heat oven to 190°C (Gas Mark 5).
4. Peel and finely dice the onion and garlic. Wash and grate the carrot. Dice the celery.
5. Heat a small frying pan and add the oil. Gently fry the onion, garlic, carrot and celery for 8 minutes until soft and without colouring. Add the chilli (if using) and paprika.
6. Combine the onion mixture with the potato and bean mixture.
7. Add the soy sauce, tomato puree and black pepper. Mix to combine and then form 4 or 8 patties with your hands.
8. Place burgers on a lightly greased baked tray and bake in the oven for 20-25 minutes, turning over once halfway through cooking time.
1 small sweet potato
1 medium white potato
1 tin kidney beans
1 tin black eyed beans
2 cloves garlic
1 celery stick
Pinch cayenne pepper or chilli flakes (optional)
1 tablespoon soy sauce
1 teaspoon smoked paprika
1 tablespoon tomato puree
Ground black pepper