Prepare cake mix according to package directions; cool. In a large bowl, whisk together the cream cheese and powdered sugar until smooth. Whisk in sour cream and rum extract. Fold in whipped topping with electric mixer. In a medium bowl, stir together sugar, coffee granules, and boiling water until dissolved; brush mixture over cooled cake. Spread cream cheese mixture over cake. Grate chocolate bar over cream cheese mixture and refrigerate. Makes 20 servings.
Approximate Nutrient Analysis per serving:
300 calories, 16 g fat, 9 g saturated fat, 30 mg cholesterol, 200 mg sodium, 33 g carbohydrate, 1 g fiber, 25 g sugar, 4 g protein