Beet-Braised Pot Roast with Horseradish and Potato Knaidlach

When the Purim revelries had passed, cooks in the Ukraine and northern Poland turned their attention to the long process of preparing rosl. They placed beets in earthenware crocks, covered them with fresh cold water, and let them slowly ferment, skimming the froth and foam weekly. A month later, a tangy, vegetal beet essence perfumed the shtetls, and the clear scarlet rosl was at last ready to be braised with pot roast and served as the popular Passover main course, roslfleisch