Slightly score the chestnuts on the side and shape in the hot oven until the shells crack.
Remove from the shells, cover with enough water in a large saucepan and cook until soft in about 50 min.
Mash the chestnuts with 4EL of the cooking water.
Heat the butter and lightly steam the mushrooms in it for 5 min until soft. Add the mashed chestnuts, red wine, cognac, bay leaf spice and thyme and simmer for 5 min on low heat. Season to taste with salt and freshly ground pepper. Remove the bay leaf and thyme and serve the sauce hot.
Our tip: Use sweet red wine for a sweet note and rather dry wine for flavorful, spicy dishes.