I've never heard of the soup before but I did some googling.
Oats are used in Polish Easter Soup (Zurek Wielkanocny)
loads of pages for it on the internet but this is one link.
Then I found the one below ? Not sure if that is what you are looking for ? I have two very old Polish Cookery books, but they are packed away at the moment. If you haven't found the right recipe in a week or two then I'll have a search through my books.
Hope you find what you are looking for :)
1/2 box Old Fashioned Quaker Oats
2 T. flour
salt to taste
1 1/2 cakes yeast
1 t. caraway seed
1 quart lukewarm water
Place oats in a large bowl. Crumble the yeast into the oats. Add the flour and then pour in the water. Stir all ingredients well. Cover the bowl and place near a warm spot to ferment all day and night. The following day, gradually add: 3 quarts lukewarm water to the same bowl; stir well. Strain through a sieve, then cook the oats slowly, stirring constantly. Add garlic and caraway seed. Keselitsa is ready when the spoon becomes coated. Serve with boiled or mashed potatoes.