Preheat oven to 375 degrees. Beat butter, granulated sugar, and brown sugar in a large bowl until light and fluffy. Beat in peanut butter, egg, and vanilla. Gradually stir in combined flour, baking powder, baking soda and salt; mix well.
Roll heaping teaspoons of dough into 1-1/2-inch balls. Place balls 2 inches apart on cookie sheet. (If dough is too soft to roll into balls, refrigerate for 30 minutes.) Dip fork into sugar; press crisscross indentation on each ball, flattening only slightly. Bake 11 to 12 minutes. Let cookies stand on cookie sheets for 2 minutes. Remove cookies to wire rack; cool completely.
Melt semisweet chocolate with 1-1/2 teaspoons shortening in top of double boiler over hot, not boiling, water. Place melted chocolate in baggie and snip bottom corner to create a small opening. Squeeze slowly to decorate cookies with a dragonfly design or create your own design.