Though distantly related to the bread and garlic soups of Spain and Italy, its base is not meat or vegetable broth, but zakwas. Zakwas is made from rye bread and water and is, in turn, distantly related both to sourdough and to Russian kvass (a fermented drink). In Poland, zakwas is available in bottles at ordinary supermarkets. Outside of Poland, you can find it in specialty ethnic markets, and even online. If you do have to make it yourself, although it sounds odd and intimidating, it is in fact extremely easy. But it does require planning a few days in advance.

Żurek can be thin and delicate or hearty, stuffed with chunks of ham, sausage, and potatoes—in which case it is really an entire meal. The Easter version always contains biała kielbasa, or “spicy white sausage,” which is the same thing as bratwurst. Sometimes żurek, like its Italian cousin, zuppa di pan cotto, is served with hard-boiled egg. But it is always sour, salty, and creamy at the same time, which makes it unlike almost anything else.

Once you’ve tried it, the taste of żurek stays with you. Over the years Anne has encountered a number of Japanese who have been to Poland (there are more than you might imagine, such is the pull of Chopin’s birthplace). Almost every single one of them specifically mentioned żurek as the one Polish food he or she would never forget. Perhaps there is some mystical link between sour bread soup and sushi; we leave that for others to interpret.

Our version is on the lighter side, and cheats somewhat by making a vegetable broth during the cooking process, instead of using plain water. We also like the spiciness of horseradish here and, perhaps for similar reasons, we prefer sausage to egg. Use Polish biała kielbasa or bratwurst if you can get it, but if not, there are many lightly spiced chicken, veal, or pork sausages that would work here. They don’t have to be precooked, as they will be boiled in the soup.