On the website madeinswietokrzyskie we can read:
“The history of Zalewajka dates back to the second half of the 19th century. It appeared in the central part of Poland and with time became popular in Świętokrzyskie and Kujawy. It was a typical peasant dish - simple and filling, which could be prepared from commonly available products. Its basic ingredients are potatoes, onions, and leaven made from rye flour. Sometimes mushrooms or pieces of sausage or bacon were added to it”
Świętokrzyska Zalewajka has been entered on the List of Traditional Products maintained by the Ministry of Agriculture and Rural Development. It is so popular in the region that it has its competition.
“The first festival of 'Zalewajka' took place in Miedziana Góra and was later moved to Bieliny. By organizing it, we want to celebrate the region's most popular soup," says Martyna Wyra from the Świętokrzyskie Mountains Tourism and Culture Tradition Centre in Bieliny.
“The competition for the best Zalewajka enjoys unflagging popularity. Each folk group adds something from themselves to the recipe - mushrooms, dill, herbs - which makes the soup unique. However, there must always be potatoes in it - this is what distinguishes "Zalewajka" from the popular Polish sour rye soup," she adds.
Source: Poland Daily 24, madeinswietokrzyskie.pl