Fermentation lies at the heart of Russian cuisine as one of the most ancient techniques of preparing food. As you will notice throughout this book, numerous recipes rely on sauerkrauts, kvass, or rassol (the fermentation liquid) for their distinct tangy flavor. This soup, which carries the name rassol in its very title, is the embodiment of such a tradition. While historically rassolnik is an old Russian dish, the go-to recipe in our family comes from Poland. Back in the 1970s, my mom took part in a school program that allowed Soviet kids to find pen pals in neighboring socialist countries. She hit the jackpot, since she was linked up with a boy in Poland (the most coveted country of all friendly socialist ones). After a few years of correspondence, my mom and her parents were invited—and most importantly permitted by the Soviet officials—to visit her pen pal. Along with a bag full of trendy garments, chewing gum, and fancy stationery, which made her the coolest teenager in school, she brought back this recipe for a good old Russian rassolnik, cooked by her Polish friend’s mom. The delicious soup always reminds me of the interwoven nature of the Soviet and Slavic histories and cuisines.