Flooding Technique

• Flooding is at least a two-stage process. The first step is to fill a pastry bag with icing, and pipe on the basic design as a line drawing. For example, if you've used a Christmas tree-shaped cutter, you might follow the outlines of the cookie. Once the lines have dried, you tint a second batch of icing and pour a small amount onto the cookie. It spreads out and fills in the area outlined by the first icing, which should be in a contrasting color. Skilled bakers can mark out multiple areas on a single cookie and fill them with different colors of icing, and finish detailed images by piping accents in contrasting colors.

The Icing

• The icing that's usually used for flooding work is called royal icing, the same kind that's used to make many of the decorations on wedding cakes. Traditionally, it is made by whipping egg whites with powdered sugar, though many bakers prefer to use dried meringue powder to ensure food safety. It dries to a hard, perfectly white matte surface, and it accepts colors beautifully. Unfortunately, although cookies decorated with royal icing can be spectacularly attractive, its blandness and disconcertingly hard texture make it less than pleasant to actually eat.

Buttercream

• Buttercream is the most universal of icings for general-purpose use, and it has the advantage of a rich and satisfying flavor. Unfortunately, its normal consistency is spreadable, rather than pourable, so it's not well suited to flooding. It also tends to stay soft, so it would be difficult to package cookies decorated in buttercream. Skilled bakers can carefully thin a buttercream by adding milk and powdered sugar in small amounts until it reaches a pourable consistency. When it's handled this way, it will form enough of a crust to be packaged. However, the thinned buttercream produces streaky, inconsistent colors that are unsatisfactory for most purposes.

Alternative Icings

• Bakers in search of an icing that's suitable for flooding but tastes better than royal icing usually turn to a form of glaze. The simplest is what professional bakers call "flat glaze" or "flat icing." It's powdered sugar whipped with milk, a small amount of vanilla, and usually a small amount of glucose or corn syrup to help keep the sugar from forming larger crystals and losing its fine texture. It accepts colors like royal icing, dries firmly enough for packaging, and is more pleasant to eat. A second type of glaze is more similar to buttercream, and contains meringue powder and a small amount of fat. Its flavor is better than that of royal icing, but it must be whipped for a very long time to minimize the risk of separation. It's also less reliable in hot weather.