Slice the mushrooms up thinly, lay them on a tray and put in the oven (at 100°C) for an hour. Cool and mix to obtain a powder.

Dissolve the syrup in a saucepan until you obtain a light syrup; deglaze with the cranberries and cook for 2 minutes, adding the balsamic vinegar; take off the heat and add the walnut oil. Leave to cool

Cook both sides of the tuna, keeping the flesh a deep pink, and arrange it on a plate, dusting it with mushroom powder and sprinkling cranberry vinaigrette on top.