From chiffon to angel food, mousses to sponges, folding is an essential technique in the world of baking. Some of my favorite desserts require this method to achieve that light-as-a-feather texture.

The pastry investigator hews to scientific method. She formulates her hypothesis: Pastry perfection rests on the ratio of flour to fat to water. She gets to work — years of false starts and soggy pies ...