Put the buckwheat in the boiling water and simmer for 20 minutes on a low heat.
Cut the meat and onion into small pieces and fry them vigorously in a little oil. Add 150 ml of water or vegetable stock and simmer for 30-40 minutes.
Season with whipped cream or crème fraîche and, if necessary, thicken the sauce with flour. Mix the flour well in cold water and add to the sauce and simmer for a few minutes.