Rye has long been a principal bread-making cereal of northern Europe. If you haven't yet experimented with rye flour, be sure to try one of the rye-based breads in this collection. But don't stop there: rye can also be used in a traditional Polish sour rye soup – and if you happen to have some rye bread left over and going stale, transform it into something sweet: Zuza Zak's Rye Bread & Chocolate Mousse.