OK, Try This at Home fans: Claire Saffitz is back for another round. She's given us bagels. We watched her make croissants. She's shown us sourdough and how to make yeasted dough. Today's lesson? Sponge cake. It may have almost broken Claire to develop, but it also may be the only cake recipe you'll ever need. Come for the baking techniques, stay for the glorious summer strawberries.