• Preheat the oven to 350°.

Cake

• To prepare the cake batter:  Combine cake mix, milk, coffee, melted butter and eggs to medium bowl and stir with an electric  mixer until well combined. Spray a 9x13 baking pan with nonstick spray and pour prepared batter into the greased pan.  Spread into an even layer.
• Bake in a preheated oven for 25-35 minutes or until a toothpick inserted in the center comes out with only a few crumbs.  Cool completely in the pan.

Icing

• Combine the butter, Nutella and milk in a small saucepan over medium heat and whisk until everything is melted and smooth.  Remove from heat, add powdered sugar and whisk until smooth.
• Add chopped hazelnuts to the frosting and stir until they are evenly incorporated. Pour the frosting over the cake.  Use a knife or spoon to move excess frosting and be sure that it is completely covered.  Allow the frosting to set up.
• Toppings
• Cut the cake into 12 squares. Add the whipped topping to a piping bag {or zipper bag} and pipe a swirl on top of each square and add a candy to each piece. Note: If you do not have a piping or zipper bag, just use a spoon to add a dollop of whipped cream to each square. Serve and store leftovers covered tightly in the refrigerator for up to 5 days.