In a large bowl, cream butter, sugars and 1/4 cup peanut butter. Added egg and vanilla; mix well. Combine flour, cocoa and baking soda; add to creamed mixture and mix well.
Blend confectioners' sugar with remaining peanut butter until smooth. Roll into 24 balls, 1 in. each. Divide dough into 24 pieces; flatten each into a 3-in. circle.
Place one peanut butter ball on each circle; bring edges over to completely cover it. (Dough may crack; reshape cookies as needed.) Place cookies with seam side down on ungreased baking sheets. Flatten each cookie slightly with the bottom of a glass dipped in sugar. Bake at 375° for 7-9 minutes or until set.