While the waffles can be eaten as soon as they are removed from the waffle iron, they will have a crispier exterior if rested in a warm oven for 10 minutes. (This method also makes it possible to serve everyone at the same time.) Buttermilk powder is available in most supermarkets and is generally located near the dried-milk products or in the baking aisle. Leftover buttermilk powder, which can be used in a number of baking applications, can be kept in the refrigerator for up to a year. Seltzer or club soda gives these waffles a light texture that would otherwise be provided by whipped egg whites. (Avoid sparkling water such as Perrier—it’s not bubbly enough.) Use a freshly opened container for maximum lift. Serve waffles with butter and warmed maple syrup.