Dice the bacon, finely chop the onion. Finely chop the chestnuts.
Clean the sprouts and cook them in the chicken stock until tender. Drain, but reserve the stock.
Put the sprouts into a blender. Add about half a glass of the stock. Process, add more stock until you get a thick, coarse mash. Cover and set aside.
Fry the onion and the bacon in little oil, until the bacon is crispy and the onion is soft. Add the chestnuts, stir-fry for about a minute.
Add the sprout mash, combine well.
Season to taste and serve.