For the venison goulash, trim the meat (remove tendons, etc.) and cut into bite-sized cubes. Also dice the onions and sauté them in a pot in not too little oil or clarified butter as slowly as possible until light, but never too dark. (The longer the onions can fry, the better the sauce will be afterwards).
Then add meat, fry briefly all around and sprinkle paprika powder on top. Deglaze with a dash of vinegar, stir in tomato paste and garlic if desired. Season with salt and pepper and add just enough water to barely cover the meat. (It should be steaming, not boiling.) Add bacon rind (gives a strong flavor) and simmer, covered, over low heat until tender, about 2 hours, depending on the quality of the meat.
Stir occasionally and add a little more water. When the meat is tender, remove the bacon rind. Stir in crème fraîche (or sour cream stirred smooth with the flour) and cook the venison goulash over moderate heat until creamy. Season again, serve and garnish each serving with a dollop of sour cream.
Spätzle or dumplings go well with the venison goulash.