Mix oatmeal with water and add the bread. Let stand at least 24 hours until it sours. Strain. Cook sausage in water for one hour. Remove sausage and skim the fat accumulated in the water. Add liquid to the oatmeal mixture. Mix in a tablespoon of horseradish. Serve hot with slices of Polish sausage and hard-cooked egg, boiled potatoes or croutons. Serves 6.
You may prefer to make this soup an easier way. Cover the sausage with 2 quarts of water and cook for 1 hour. Remove sausage, cool water and set in refrigerator over night. The next day remove the fat, salt to taste, add 2 tablespoons vinegar or lemon juice, 1 tablespoon horseradish and thicken with 2 tablespoons flour mixed with 1 cup sweet cream. Bring to boiling point and serve hot as above.