Preheat the oven to according to package instructions for a 9x13” pan. Coat baking dish with canola oil or cooking spray.
To make the batter: Prepare the batter according to box instructions. Pour the batter into the prepared dish and set aside.
To make the filling: Combine the mascarpone, ricotta, egg, sugar, and salt in a bowl of a stand mixer and whisk until smooth. Gently pour the filling onto the cake batter so the top is completely white.
Bake cake until a skewer inserted in the center comes out clean and the chocolate layer has risen to the top, about 40 minutes. Let the cake cool before frosting it.
Just before serving, make the frosting: In a stand mixer, blend together the mascarpone, chocolate pudding mix, sugar and milk in a small bowl until smooth. Using an offset spatula, spread the frosting evenly all over the cake and serve.
Prep Time: 15 minutes
Cook Time: 40 minutes
Inactive Prep Time: 30 minutes
Ease of preparation: intermediate
Active Time: 55 minutes
Total Time: 1 hour 25 minutes