"You see how it's so smooth? That's the first rule," says Payard as he leans over a glass bowl, stirring an egg white into a blend of almond flour and powdered sugar. He's showing Wu how to make a macaronade, the base for the meringue sandwich cookies called macarons. Wu is a gifted fashion designer (he created the inaugural gown for Michelle Obama) and an ambitious home cook. But the one time he made macarons, he mistakenly used almond paste instead of almond flour, rendering them fatally lumpy.