Start by making the mayonnaise. Whisk the egg yolks, mustard and vinegar together in a medium bowl until smooth. Slowly pour the vegetable oil into the bowl, starting with a little drizzle and whisking well. This is easiest to do with an electric hand whisk. Continue to drizzle in the remaining oil, whisking all the time, until the mixture has thickened. Season to taste.
Put the crab into a large bowl with the potatoes, spring onions, chives, lemon juice and egg yolk. Season and mix everything together well. Divide the mixture into 8 portions. Dust your hands with flour and form each into a round fish-cake shape roughly measuring 8–10cm in diameter and 2cm thick.
Heat a large, non-stick frying pan over a medium heat until hot. Drizzle with a little oil and pop the fish cakes in. Cook for 2–3 minutes on each side until golden and heated through. You may need to do this in batches, depending on how big your pan is.
To serve, pop 2 crab cakes onto each plate, garnish each with watercress and a lemon wedge and serve with a dollop or a little pot of mayonnaise.
Extracted from James Martin’s Great British Adventure by James Martin (Quadrille, £25) Photography © Peter Cassidy
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