Boil the sour cream in a large saucepan. Sieve in half of the flour and stir it well to make a non-lumpy porridge. Bring it quickly to the boil again so that butter is separated out from the porridge. Scoop off the fat using a ladle and set it aside for use later on. Sieve in the remaining flour and add the salt. When the porridge has been brought carefully to the boil again and contains no lumps, it is ready to be served. Serve in deep plates, pour a bit of fat on top and sprinkle with butter and cinnamon. It is customary to serve sour-cream porridge with cured meats and a squash made from red berries. Serves 6.