Pâte à Choux dough is a mechanically leavened dough that can expand when baked, leaving a large cavity in the center. It is the most unusual dough in this book, beginning as a roux (the same mixture of flour and butter used to make sauces) that cooks on the stove before being baked. Choux is also the only dough that can be—and in fact often needs to be—piped. The dough ratio is 6 FLOUR : 4 FAT : 8 LIQUID : ½ SUGAR : 7 EGG.