Preheat your oven to 180°C (356°F). Grease and line two 8-inch round cake pans. In a mixing bowl, combine the Dr. Oetker Chocolate Pie Filling & Dessert Mix, flour, and Dr. Oetker Baking Powder. Add the softened butter, caster sugar, Dr. Oetker Vanilla Sugar, eggs, and milk. Mix with an electric mixer on the lowest speed briefly, then on the highest speed for 2 minutes until a smooth batter forms. Divide the batter evenly between the prepared cake pans.

Bake the cake layers for about 40 minutes or until a toothpick inserted in the center comes out clean. Remove from the oven and allow the cake layers to cool in the pans for 10 minutes. Transfer the cake layers to a cooling rack and let them cool completely before frosting.

For the frosting, place the heavy cream and remaining Dr. Oetker Chocolate Pie Filling & Dessert Mix in a saucepan. Stir continuously over medium-high heat to prevent burning. When the mixture comes to a boil and begins to thicken, stir for an additional minute. Remove from heat, stir well two separate times over a 5-minute period and let cool to room temperature. In a mixing bowl, whip the cooled chocolate mixture and softened butter with an electric mixer until smooth and creamy.

Once the cake layers have cooled completely, spread a generous layer of frosting on top of one cake layer. Place the second cake layer on top and frost the top and sides of the cake. Decorate as desired with chopped chocolate and refrigerate until ready to serve.