Boil the potatoes until tender. Drain and mash them with plenty of salt and butter.
Preheat the oven to 200 C / Gas 6.
Finely chop the onion, garlic, chilli, spring onions, coriander and prawns. Mix in a bowl with the crabmeat, cumin, breadcrumbs, mayonnaise if desired, and mashed potato.
Break an egg into the mixture and ensure it is thoroughly mixed through. Shape the mixture into little round cakes.
Bake in the oven for about 20 minutes, turning them over halfway, or until they turn a golden brown colour. Alternatively, pan fry them for a few minutes until the same golden brown colour is achieved.