Peel the shallots and cut them into pieces. Halve or quarter the chestnuts. Sweat both in butter and deglaze with a dash of wormwood. Top up with the vegetable stock and cook until soft.
Puree the soup with the blender. If it is too thick, add a little more stock or water.
Cut the bacon into cubes or strips, add to the soup with the rosemary and let it steep a little. In the meantime, whip the whipped cream until semi-firm.
Finally, fold the whipped cream into the soup, but do not let it boil again.