Preheat your oven to 350°F (175°C). In a large mixing bowl, combine the chocolate cake mix with the required ingredients as per the package instructions. Add vanilla extract for extra flavor.

Pour the prepared batter into a greased 9×13-inch baking dish and bake for 25–30 minutes. Check doneness by inserting a toothpick; it should come out clean.

While the cake cools, prepare the filling by whisking together peanut butter, sweetened condensed milk, and whole milk until smooth.

Poke holes evenly across the surface of the warm cake with a wooden spoon to allow the filling to absorb.

Slowly pour the creamy peanut butter mixture over the top of the warm cake, allowing it to seep into the holes.

In a chilled bowl, beat heavy cream and powdered sugar until soft peaks form. Fold in remaining peanut butter for a smooth whipped topping.

Spread the creamy peanut butter topping over the cooled cake, covering it entirely. Top with chopped Reese’s cups and crushed peanuts.

Melt chocolate and peanut butter together, drizzle over the topped cake, and refrigerate for at least 1 hour.