PREPARATION:

1. Beat butter, shortening and peanut butter in large bowl at medium speed of electric mixer. Gradually add powdered sugar, beating until smooth. Add egg yolk and vanilla; beat well. Add flour; mix well. Stir in 1/3 cup ground peanuts. Cover dough; refrigerate 1 hour. Prepare Peanut Buttery Frosting.
2. Preheat oven to 350°F. Grease cookie sheets. Shape dough into 1-inch balls. Place 2 balls, side by side and slightly touching, on prepared cookie sheet. Gently flatten balls with fingertips to form into "peanut" shape. Repeat steps with remaining dough.
3. Bake 16 to 18 minutes or until edges are lightly browned. Cool on cookie sheets 5 minutes. Remove cookies to wire racks; cool completely.
4. Place remaining 2/3 cup ground peanuts in shallow dish. Spread about 2 teaspoons Peanut Buttery Frosting evenly over top of each cookie. Coat with ground peanuts.