- Peel the sweet potatoes and potatoes and cut into chunks. Place in a pan of salted cold water and bring to the boil and cook for 15 minutes. Drain, mash and then leave to cool.
- Put the fish in a saucepan of cold water to cover and bring up to the boil. Then turn off the heat and leave covered for 6-8 minutes to cook gently. Remove from the pan and leave to cool until you can flake in to the potato mixture.
- Stir in the chopped chilis and coriander and season to taste.
- Shape the mixture in to 6 balls and if you can, press into circle moulds so that each fishcake is the same size. Place them in the fridge to cool until ready to cook.
- When ready to fry, heat the olive oil in a pan. Pour the polenta on to a plate and roll each fishcake in the polenta to coat. Fry for 4-5 minutes on each side. They can now be served but if you wait, you can place them in a pre-heated oven 140Fan/160C/Gas 4 for up to 20 minutes just to keep them warm.
- Meanwhile, mix the mayonnaise with the wasabi. Serve with the fishcakes.
Adapted from a recipe from Delicious Magazine