Cook the sweet potatoes in boiling salted water for 10-15 minutes. Meanwhile, poach the cod fillets in a shallow pan of simmering water for 7-10 minutes, until cooked through and flaky.
Once cooked, drain the sweet potatoes and return them to the pan to steam dry for 5 minutes. Mix in the butter, coriander and seasoning, mashing with a fork until light and fluffy.
Once the cod has cooked through, remove from the pan with a slotted spoon and allow to cool a little, then flake into the mash and mix until evenly distributed.
With floured hands, shape and press the fishcake mixture into 8 even-sized patties and set aside.
Put the flour, egg and breadcrumbs into three separate dishes and dip the fishcakes in each, first coating in the flour, then the egg, then the breadcrumbs.
Arrange the coated fishcakes on a tray and chill for 30 minutes.
While the fishcakes are chilling, make the tomato salsa. Pre-heat the oven to 200°C. Place the tomatoes in a small baking dish and drizzle with the balsamic vinegar and olive oil. Season well, then roast for 15-20 minutes. Once cooked, roughly chop the tomatoes (leaving the oven on) and add to a serving bowl, pouring over any leftover juices from the baking dish. Set aside until ready to serve.
When the fishcakes are chilled, grease a baking tray generously with some of the oil and add the fishcakes. Brush over the rest of the olive oil, then bake in the oven for 25-30 minutes, until cooked through.
To serve, arrange the cooked fishcakes on a plate and serve with the salsa, lemon wedges and mixed leaves.
