Heat oven to 375 degrees. Reserve 1/3 cup frosting. In large bowl, combine remaining frosting, peanut butter and egg. Blend well. By hand stir in flour. Shape dough into 1 inch balls. Place 2 inches apart on ungreased baking sheet. With the bottom of glass dipped in sugar, flatten each ball to 2 inch diameter.
Bake until set - about 4 to 7 minutes. DO NOT OVERBAKE. Cool 1 minute. Remove from sheet, then cool completely. Lightly frost with reserved 1/3 cup frosting.