1) Cook the potato until soft; allow time to cool.
2) While the potato is cooking, place the granulated stevia or sugar in a blender and add the cornstarch. Blend until powdery.
3) Once the potato has cooled, place it in a bowl with the powdered stevia/sugar and vanilla extract. Adding 1 tablespoon at a time, mix in the soymilk powder until desired frosting consistency is reached.
Source of recipe: In an attempt to rid the world of "guilty pleasures", I engineered a "guiltless pleasure" frosting that, for the sake of argument, tastes very guilty.