Chill the crab in the freezer for one hour to humanely put it to sleep.
Boil the crab in salted water for 12 minutes and leave to cool on a tray.
Peel, rinse, and boil potato pieces for 10-15 minutes until tender, then drain and mash.
Extract white crab meat, discard shell fragments, and chill in a bowl.
Mix lemon zest, parsley, garlic, egg yolk, Tabasco, and crab, then incorporate mashed potato and season.
Shape the mixture into 18 small cakes and chill until ready to cook.
Whisk egg yolks, mustard, and lemon juice, then slowly incorporate oil to create mayonnaise.
Flour the cakes and fry in hot oil until golden-brown and heated through.
Serve three cakes per person with watercress, lemon quarters, and the prepared mayonnaise.