Place the meringue powder and water in the bowl of a stand mixer using the paddle attachment. Beat until it is combined and foamy.
Sift in the powdered sugar and beat on low to combine. It will probably be helpful to add the powdered sugar in 3 additions so that powdered sugar doesn't get all over the kitchen. Do not skip the sifting. Powdered sugar frequently has clumps. If powdered sugar is added without sifting, the royal icing will have lumps that may not break up during mixing.
Once combined, add in the vanilla extract and the corn syrup (which helps to keep the royal icing shiny).
Increase the speed to medium-high on the stand mixer and beat for approximately 5 minutes (or until the icing forms stiff peaks).
Cover the stand mixer bowl with plastic wrap. Make sure the plastic wrap touches the surface of the royal icing so that the surface doesn’t dry and harden.
Divide the royal icing and color with gel paste food colorings, if desired.
If you need a thinned icing, add water to the “stiff” royal icing a teaspoon at a time. The consistency can change quickly if you add too much water. Add the water until you have the consistency you need to decorate the dessert.
