Heat oven to 350°F. In large bowl, break up cookie dough. Stir or knead in 1/4 cup flour and the cocoa until well blended. Remove half the dough, and refrigerate remaining dough until needed.
Sprinkle 2 tablespoons flour onto work surface. With rolling pin, roll dough 1/8 inch thick. With 2 1/2-inch heart-shaped cookie cutter, cut out heart shapes. On ungreased cookie sheets, place shapes 1/2 inch apart. Repeat with remaining dough and flour.
Bake 10 to 12 minutes or until set. Remove cookies from cookie sheets to cooling racks. Cool completely, about 5 minutes.
In small bowl, mix frosting and peppermint extract until well blended. Spread about 2 teaspoons frosting on each cookie. Sprinkle each with about 1/4 teaspoon crushed candy.