Step 1: Prepare the Cake
1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour a 9×13-inch baking pan.
2. Mix Cake Batter: In a large mixing bowl, combine the chocolate cake mix, water, vegetable oil, and eggs. Beat on medium speed for about 2 minutes, until well combined.
3. Bake: Pour the batter into the prepared baking pan and smooth the top. Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted in the center comes out clean. Remove from the oven and let it cool in the pan for about 10 minutes.

Step 2: Make the Peanut Butter Filling
1. Mix Filling Ingredients: In a medium bowl, beat together the peanut butter, powdered sugar, softened cream cheese, vanilla extract, and milk until smooth and creamy. Adjust the milk as needed to achieve a spreadable consistency.
2. Spread Filling: Once the cake has cooled slightly, spread the peanut butter filling evenly over the top of the cake.

Step 3: Prepare the Chocolate Topping
1. Heat Cream: In a small saucepan over medium heat, heat the heavy cream until it just begins to simmer. Remove from heat.
2. Melt Chocolate: Add the semi-sweet chocolate chips to the hot cream and let it sit for about 2 minutes. Stir until the chocolate is completely melted and the mixture is smooth.
3. Pour Topping: Pour the chocolate topping over the peanut butter layer, spreading it gently to cover the entire surface.

Step 4: Cool and Serve
1. Cool the Cake: Allow the cake to cool completely at room temperature, then refrigerate for at least 1 hour to set the layers.
2. Garnish: Before serving, sprinkle chopped peanuts on top for added crunch and flavor (optional).
3. Slice and Serve: Cut into squares and serve chilled or at room temperature.