(from Beckshe’s recipe box)
- 2 1/8 c. powdered sugar
- 2 egg whites
- 1/2 tsp. salt
- 2 tsp. vanilla
Place all of the ingredients except the sprinkles in a large bowl and beat until stiff and glossy, about 10 minutes. The resulting icing should be the perfect consistency for piping, but if not, beat in more powdered sugar until it is.
Using a piping bag fitted with a small, plain tip, pipe a border around the edge leaving a 1/4" margin. Allow to dry for about an hour.
Thin remaining icing by adding water to it in 1 tsp. increments until a trail of icing from a spatula disappears in 3 seconds. Flood the border you piped earlier with a small amount of icing, using a small offset spatula or toothpick to reach to corners. Allow to dry 3 minutes before adding sprinkles, then overnight before eating.