1) Cut beans and potatoes into 1" chunks and cook in about 6 cups of salted water. 2) Add onion, garlic, parsley, oil, and flour. 3) Heat, stirring, without boiling. 4) Remove from heat and add 1/2 cup cold water, vinegar to taste, and sour cream. 5) Do not heat - stir well, and serve. More vinegar may be added to taste.