Soak the quail beans overnight. Tilt away the soaking water after soaking. Simmer the quail beans for approx. 60 - 90 minutes according to the instructions on the packet. Then drain.
Toast the flour in a saucepan without fat until dark. Pour hot stock, stirring constantly. If there are lumps, use the hand blender to help so that everything is smooth. Add vinegar and simmer for a few minutes. Season to taste with sugar, salt and pepper.