Beat butter, sugar and vanilla in large bowl until creamy. Stir together flour and cocoa; gradually add to butter mixture, stirring until well blended. Cover dough with heavy foil and refrigerate at least 1 hour, or until firm enough to handle and shape.
Heat oven to 375 degrees F. While oven is heating, unwrap chocolate kisses. Mold a scant tablespoon of dough around each chocolate piece, covering completely. Shape into balls. Place on ungreased cookie sheet.
Bake 10 to 12 minutes or until set. Cool about 1 minute and remove from cookie sheet to wire rack. Cool completely. Roll in powdered sugar. Roll in sugar again just before serving.