- Cut the fennel into eight pieces, place them in a sous-vide bag with 40g of butter with seaweed and bonito flakes, the juice of half a lemon, close and cook for 40 minutes at 75°C. Stop cooking by immersing the bag in an ice water bath.
- Rinse the potatoes and bake them for 2 hours in a preheated oven at 190°C. Push them through a strainer to remove the skins and mix in 30g of butter with seaweed and bonito flakes and 150g of hot milk using a potato masher for at least 2 minutes
- In a small saucepan, boil the water, mustard seeds, rice vinegar, sugar and bay leaf for 10 minutes.
- In a frying pan over a low heat, melt 20g of butter with the seaweed and bonito flakes, then place the sole fillets and brown them by basting them regularly with butter (add butter if necessary)
- In a hot frying pan, melt a little butter and fry the pieces of fennel on one side only.
- Place a sole fillet on each plate with some of the cold mustard seeds, mashed potatoes and fennel.