Turn sugar into mixing bowl.
Combine boiling water with butter; when melted, add vanilla.
Add to sugar and beat until smooth.
Then add more boiling water if necessary, drop by drop to produce a smooth spreading consistency.
Beat 2 or 3 minutes until very creamy, keeping sides of bowl scraped down.
Spread immediately on warm cake.
This frosting is frequently used for coffee cake, buns, doughnuts, and simple one layer cakes.
Strained lemon juice or other fresh fruit juice may be substituted for water and vanilla if desired.
Enough for two 8-inch cakes.