The flavor comes from high-quality real vanilla extract, the sweetness from a combination of granulated sugar, powdered sugar and corn syrup, while the frosting’s light texture comes from whipped egg whites — not raw, but cooked in a double boiler.
The original recipe author cautions to be sure that the egg mixture is cooled completely before you fold it into the buttercream icing mixture.
How to make a good old-fashioned fluffy vanilla frosting
Adapted from the Montgomery Advertiser (Montgomery, Alabama) December 2, 1955
Really good, old-fashioned frostings — this is one of the pleasant things of grandma’s day that can stand some re-creating today.
In flavoring, she knew that only the true, pure vanilla extract would give a cake the delicate flavor and freshly baked fragrance that would make her a prize-winner.