Rinse and peel the vegetables on the broth. Fold in a deep pan, add the roots, bay leaf, pepper and pour 1 liter of water.
Put on a big fire and let it boil, remove the noise if it appears. Reduce the heat and let it boil for 20-30 minutes. Tighten the fire to a minimum, cover and let stand for another 5 minutes. Strain the broth, discard the vegetables.
Chop the onion finely, cut the mushrooms into slices. Heat in a deep frying pan OM and simmer in it mushrooms with onions until soft (20 min). Add chopped basil, salt and pepper.
Put the mushrooms in a pan, pour in the broth and let it boil. Puree with a hand blender, pour in the cream, return to the fire and let it boil again.
Pour into plates, garnish with basil and freshly ground black pepper.