Heat the oven to 180°.
Place the chestnuts on an oven tray and cover with olive oil and roast them for 15 mins. Keep 50g aside for dressing the soup.
Peel and slice the onions and steam cook them for 10 minutes.
Place the onions and the roasted chestnuts in a blender.
Grate some of the tonka bean, add nut oil and the hot vegetable broth, season with salt and petter and the cardamon. And then mix until you have a smooth texture.
Reheat for 5 minutes at a low temperature.
Pour into the soup bowls and decorate with the chestnuts. Chop up some hazelnuts and add to the top. Pour a dash of walnut oil before serving.