1. Heat oven to 350°F.
2. Beat butter, peanut butter, granulated sugar and brown sugar in large bowl until well blended. Add egg and vanilla; beat well. Stir together flour, baking powder, baking soda and salt; gradually beat into peanut butter mixture. Shape dough into 1-inch balls; roll in chopped peanuts, if desired or granulated sugar. Place on ungreased cookie sheet.
3. Bake 8 to 10 minutes or until cookies are set. Immediately press one chocolate piece into center of each cookie; cookies will crack around edges. Remove from cookie sheet to wire rack. When chocolate has melted (about 1 to 2 minutes), press 2 to 3 peanut halves into chocolate. Cool completely. Makes about 48 cookies.