"Puff pastry takes longer to cook than you think," says chef Alex Guarnaschelli. "It looks browned and ready on the outside but still be underdone in the middle. So let it cook! Dusting it with sugar for baking (or even running it under the broiler with sugar once cooked) caramelizes the outside of the pastry … So tasty! When you cut the millefeuille, use a serrated knife and a sawing motion to cut even (and fairly neat) portions. Or just put in the center of the table with some forks and let things happen as they may."