Beat in 1/2 cup peanut butter, 1/4 cup butter or margarine, and shortening in a large mixing bowl with an electric mixer on medium speed for 30 seconds. Add brown sugar and baking powder; beat until combined. Beat in egg and 1 teaspoon vanilla. Beat in as much of the flour as you can with the mixer. Stir in remaining flour with a wooden spoon. Divide dough in half. Wrap and chill for 2 hours or until easy to handle. (Dough can be chilled overnight.)

Roll out each portion of dough on a lightly floured surface until 1/8 inch thick. Transfer a peanut-shape pattern to heavy paper. Place pattern on dough and cut out with a sharp knife. Place cutouts 1 inch apart on an ungreased cookie sheet.

Bake in a 350 degree F oven for 8 to 10 minutes or until bottoms are lightly browned. Transfer cookies to wire racks to cool.

For the frosting, in a medium bowl beat together 1/4 cup butter and 1/3 cup creamy peanut butter until combined. Beat in powdered sugar, 1/2 teaspoon vanilla and enough milk (3 to 4 teaspoons to make spreading consistency. Drizzle over sandwiches. Makes about 36 sandwich cookies.

For the peanut shaped pattern, the peanut shape should be 4-inches long, 1 1/2-inches wide, and with an indention of 1-1/4-inches in width in the center.