Preheat the oven to 350° F and grease a 9 x 13 inch baking dish with butter or nonstick cooking spray. Set aside.
In bowl of an electric mixer (or use hand mixer), cream together the butter and sugar.
1 cup salted butter, 2 cups granulated sugar
Once the sugar and butter are thoroughly creamed together, add the eggs and milk.
4 large eggs, ½ cup whole milk
Continue mixing until the mixture is smooth and homogenous.
In medium-sized mixing bowl combine baking powder, baking soda, flour, and half of the hot chocolate powder. A cup at a time, add the dry mixture to the wet mixture and mix to combine.
1 teaspoon baking powder, ½ teaspoon baking soda, 3 cups all-purpose flour, ½ cup hot chocolate powder
Pour the cake batter into the baking dish and bake for 50 minutes.
Remove the cake from the oven and use the handle of a wooden spoon to poke holes throughout the cake. Whisk the remaining hot chocolate powder and the heavy cream together until smooth. Pour the mixture over the top of the cake.
1 cup heavy whipping cream
Allow the cake to cool for 1 hour in the fridge. Once cooled, top with the whipped frosting.
24 ounces whipped chocolate frosting