For the Cake Base: Preheat your oven to 350°F. Grease a 9x13 inch baking dish. Prepare the chocolate cake mix as directed on the box and pour the batter into the prepared pan. Spread evenly.
For the Ricotta Layer: In a large bowl, mix ricotta cheese, eggs, sugar, and vanilla extract. Mix until smooth. Pour this mixture over the chocolate cake batter. Don’t worry if it seems too liquid; the layers will switch during baking.
Baking the Magic: Place the pan in the oven and bake for 60 minutes. Do not open the oven door during baking. The cake is done when the top is set and lightly golden.
Cool the Cake: Once baked, remove from the oven and cool completely at room temperature. Refrigerate overnight before adding the topping for best results.
For the Chocolate Mousse Topping: Prepare the chocolate pudding with cold milk according to package instructions. Once set, gently fold in the Cool Whip to achieve a mousse-like consistency. Spread the mousse evenly over the cooled cake.
Chill and Serve: Cover and refrigerate for at least 6 hours, or preferably overnight, before serving.