Open the sea urchins by slicing a lid and leaving the urchin’s shell intact, so it can be stuffed with the potato salad. Spoon out the coral and reserve.

In a bowl, mix the egg yolks, salt, white pepper and lemon juice. Beating constantly, add the olive oil in a thin stream to emulsify the mixture. Add two tablespoons of tepid water towards the end.

Roughly chop the potato and mange-tout into chunks, dress with the mayonnaise and chopped fennel top.

Mix the reserved coral into the potato mayonnaise and stuff inside the sea urchins.