1) Remove membrane if liver is not thinly slices. Wrap in wax paper and freeze overnight.
2) Cut slantwise into thin slices.
3) To prepare barbecue sauce, mix together tomato puree, vinegar, Worcestershire, garlic, salt, cayenne, and water.
4) In a bowl mix flour, salt, and pepper and dredge liver pieces in it.
5) Add to the skillet and quickly brown.
6) Mix in barbecue sauce and cook, covered, for about 3 minutes. Do not overcook liver.
7) Add seasoning to taste.