Melt 20g butter in a saucepan (or a large pan) and add the carrots. Sprinkle with the sugar and cook for about 5 minutes. Salt and pepper.
Deglaze with the wine, add 6 tablespoons of cream and cook covered until the carrots are firm to the bite.
In the meantime, sauté the mushrooms in hot butter, season.
Now mix the carrots, mushrooms and half of the parsley, place in an ovenproof dish, drizzle with the remaining cream, place the cheese on top and put in the hot oven (200 ° C).
After about 6 minutes, take the gratin out of the oven and sprinkle with the remaining parsley.