Boil the potatoes in salted water for 15 minutes until tender, drain, add half of the butter and mash well. Meanwhile cook the Brussels sprouts for 5 minutes until just tender, drain, cool and shake dry and shred finely.
Heat the remaining butter in a frying pan and fry the onion until just soft, cool slightly and add to the mashed potato.
Mix the sprouts with the turkey, potato and cooked onion and season to taste. Leave until cool enough to handle then shape into 8 cakes.
Tip the flour onto a plate, coat the cakes, and gently tap off the excess flour.
Heat a large frying pan and shallow fry the cake in rapeseed oil, do this in batches for 4 minutes each side, turning carefully.
Drain on kitchen paper and transfer to a baking sheet lined with greaseproof paper.
Serve with a little rocket, poached eggs, red pepper sauce and rocket.
To make the red pepper sauce, heat the oil in a saucepan and add the onion and garlic, fry over a low heat until the onion has softened. Add the red peppers and cook until they are heated through. Transfer the mixture to a food processor, add the vinegar and sugar and season with sea salt and black pepper, blend until smooth. Add a little water if you require a thinner consistency.
Serve warm or cold. This sauce will keep for up to 5 days in a fridge or freeze any sauce leftover.
Tip: You can use leftover mashed potato and cooked Brussels sprouts.