Preheat the oven to 180°C, fan 160°C, gas 4. Put the cod on a lined baking tray and cook in the oven for 15-20 minutes until cooked through. Remove from the oven and leave to cool slightly.
While the cod is baking, put the potatoes in a pan of cold water, bring to the boil and cook for 10-15 minutes or until tender. Drain and mash with the milk until smooth.
Meanwhile, gently heat 1 tablespoon of the vegetable oil in a small pan and cook the shallots until softened.
Put the cooked fish, mashed potato, cooked shallots, Thai paste and coriander in a food processor and blend until smooth. Gently roll the mixture into 20 small balls, then flatten slightly and dust with flour. Chill in the fridge for 30 minutes.
Put the eggs in a shallow bowl and the breadcrumbs in another. Roll the fish cakes in the egg, then the breadcrumbs.
Heat the remaining oil in a non-stick frying pan, and fry the fish cakes over a medium heat for 3 minutes, turning once, until golden. You will need to do this in batches.
Serve on a platter with the sweet chilli sauce and lemon wedges.