For the lime mayonnaise
Whisk the egg yolks with a pinch of salt and the juice of half a lime. Add the oil a little at a time to produce a glossy mayonnaise that is as smooth as thick cream, finally add the other half of the lime juice and its green zest.
For the hot dog
Put the sea-bass through the cutter with the bread, taking care to squeeze it out first, and the marjoram; season with salt, pepper and Grana Padano cheese.
Soak the gelatine sheet until it softens and add it to the slightly warmed sea urchin pulp. Then add the potato and lemon juice. Roll out the mixture to a thickness of 1/2 centimetre and freeze it.
Put the sea-bass mixture into a forcing bag, cut the nozzle end to a diameter of 3 centimetres and form cylinder shapes about 10 centimetres long.
Insert the filling in the middle while still frozen, previously obtained by cutting the sea urchin sliver 6/7 centimetres long and a few millimetres wide. Brown the hot dog in a frying pan with just a little oil before finishing it off in an oven at 180° for 3 minutes.
In the meantime, keep the bread warm, cut it lengthwise, add the sauerkraut and mayonnaise and then place the hot dog in the centre.
Serve on a plate with the ketchup and topinambur chips, previously washed, cut into rounds, left to soak in water with a hint of salt, drained and fried in oil at 170°C.