Horseradish Wash, peel and grate. Sprinkle with vinegar. Of the butter and flour make a light roux, pour in meat stock and bring to the boil. Add horseradish and sour cream, seasoned with sugar, vinegar and salt. Then add the yolks and mix well, it should not boil. The sauce is suitable for boiled beef soup with meat, beef tongue or boiled fish.