Preheat the oven to 350°F (175°C) and prepare a 9×13-inch baking dish by spraying it with nonstick cooking spray.
In a large bowl, mix together the cake mix, water, vegetable oil, and egg whites using an electric mixer on medium speed for 2 minutes.
Pour the batter into the prepared baking dish and bake for 29-34 minutes, or until a toothpick inserted into the center of the cake comes out clean.
While the cake is baking, whisk together the High Brew Cold Coffee and sweetened condensed milk in a medium bowl.
Once the cake is out of the oven, immediately poke holes into the top using the end of a wooden spoon, spacing them about 1½ inches apart.
Whisk the coffee mixture again and gently pour it evenly over the top of the cake, using a ladle if needed.
Refrigerate the cake until completely cooled, about 30 minutes to 1 hour.
In a mixing bowl, whip the mascarpone cheese for about 3 minutes until smooth and slightly fluffy. Add the vanilla frosting and beat together until fully combined.
Spread the mascarpone frosting over the cooled cake.
Use a zester or grater to shave the unsweetened chocolate over the top of the cake for garnish. Serve chilled and enjoy!