Prepare the border icing: Mix together the powdered sugar, vanilla, and 2 tablespoons of milk or water for the border icing using a spoon or a fork. It should be quite thick, and if you drizzle a little from your spoon, the ribbon should hold for a few second before melting back into the icing. This border icing should be just thick enough to pour easily. If desired, add food coloring to this border icing now.