Caramelize the powdered sugar in a saucepan until light brown. Pour in the stock, add the chestnuts and simmer for about 30 minutes over a very low heat. Finely puree with a hand blender, add salt and pepper, add 150 ml of cream and creme fraîche and the tablespoon of truffle butter, mix until frothy.
Heat 50 ml of cream and the teaspoon of truffle butter with a pinch of salt, mix very frothy with a hand blender.
Serve the soup in glasses, put the mixed cream on top as a head.
Sprinkle a little cayenne pepper or chilli threads on top, if desired for the look.