Mix the mashed potato with the spring onions, mayonnaise, lemon zest and juice then gently fold in the white crab meat and seasoning. Divide the mixture into 8 then shape into cakes. Place into the fridge to firm up. After 30 minutes remove from the fridge, lightly flour them then dip in the beaten egg then the fine oatmeal, shaking off any excess as you go.
For the salad, blanch the tomatoes for 30 seconds in boiling water then place straight into ice cold water. Remove the skins and the seeds and cut into chunks. Mix with the finely sliced red chilli and red onion, the coriander leaves and the olive oil. Season with salt and pepper and leave at room temperature for an hour or so. Heat a frying pan until hot, add the veg oil, heat, then carefully place in the fishcakes. Once golden brown on both sides transfer them to a baking tray and place into a 170C oven until hot in the centre (6 mins or so).
For the chive butter sauce, boil the stock until reduced to about 100ml. Turn down the heat, add the butter and whisk (or use a stick blender) until the butter is amalgamated and the sauce light and slightly thickened. Stir in the lemon juice and seasoning, then the chives. Keep warm but do not let it boil or it will split.
Spoon the tomato salad onto the centre of the plate, top with two fishcakes and finish with the chive butter sauce drizzled round.
Impress your guests with these crab cakes which look and taste amazing.