Cut the onions into fine rings, sauté lightly in butter, sprinkle with coarse pepper, extinguish with a few splashes of vinegar, fill with milk, let bubble.
Add the clear soup and boil everything together to a creamy sauce.
Fold in the grated horseradish, season with a little sugar and, if desired, round off with condensed milk or whipped cream.
Serve with boiled meat, as well as roast mutton or lamb.
Note: Flour is listed in the ingredients, but not in the instructions. It is assumed that the onion rings are dusted with flour before or after steaming in butter.