Preheat the oven to 350 degrees Fahrenheit and grease a 9x13 inch baking pan with cooking spray.

In a large mixing bowl, beat together the cake mix, eggs, Dr Pepper and vegetable oil, just until combined, about 1 minute.

Fold in the mini chocolate chips and then pour the cake into the prepared pan and spread into an even layer.

Bake for 27-35 minutes or until a toothpick comes out clean, the cake bounces back when tapped or the cake reaches 210 degrees Fahrenheit internally.

Allow the cake to cool for 10-15 minutes while you make the frosting.

Place the melted butter in a medium sized mixing bowl and slowly whisk in the milk until a creamy mixture forms. If the butter starts to clump, warm the bowl with a hot towel while whisking.

Add in the cocoa powder and whisk until smooth and combined, 1-2 minutes. If the butter clumps, you can warm the bottom of the bowl with a hot towel or slowly heat the frosting in 10 second increments until it melts and you get a smooth mixture.

Add the powdered sugar, ½ cup at a time, whisking continuously until smooth and completely incorporated.

Slowly mix in the vanilla until smooth.

Spread the frosting over the cake and then sprinkle on the nuts.

Slice and serve warm with vanilla ice cream or whipped topping, optional.