Heat oven to 350ºF. In large bowl, break up cookie dough. Add cocoa; knead into dough with hands until well combined.
Reshape dough into 12-inch log. Using sharp knife, cut log into 24 (1/2-inch) slices. On ungreased cookie sheets, place slices 2 inches apart.
Bake 10 to 12 minutes or until edges are light brown. Cool 2 minutes; remove from cookie sheets to cooling racks. Cool completely.
Meanwhile, in 2-cup glass measuring cup, microwave cream and corn syrup uncovered on High 1 minute. Stir in chocolate and butter until chocolate is melted. Let stand about 30 minutes. Cover; refrigerate about 30 minutes or until spreading consistency.
When cookies are completely cooled, spread Ganache on bottom of 1 cookie; top with second cookie bottom side down. Repeat with remaining cookies.