Combine graham cracker crumbs from cheesecake mix, butter, and sugar. Firmly press mixture in bottom and up sides of a 9" pieplate.
Combine milk and chocolate syrup in a medium bowl, stirring well. Add cheesecake filling mix; beat at low speed of an electric mixer until blended. Beat at medium speed 3 minutes. Fold in finely chopped chocolate. Spoon into prepared crust. Cover and chill at least 1 hour. Garnish, if desired. Before serving, dip bottom of pieplate in hot water for 30 seconds.
Note: For cheesecake mix, we used Jell-O brand. For chocolate mint-flavored syrup and chocolate bars, we used Hershey's.