– Cut the truffle strips into small cubes and marinate with the olive oil, ideally 1 or 2 days beforehand, if not 1 hour before.
– Wash and peel the celery and potatoes, then cut into cubes. Place in a saucepan of salted water, bring to the boil and cook for 15 minutes, turning down the heat. Check for doneness by inserting a knife.
– Drain and purée, adjusting the seasoning.
– Salt and roll up the sole fillets, holding them in place with a wooden skewer.
– Steam for 10 minutes.
– Serve two sole fillets per person with mashed potatoes, drizzled with truffle oil.