Preheat your oven to 350°F (175°C) and grease two 9-inch round cake pans.

In a large bowl, combine the chocolate cake mix and peanut butter. Add water, eggs, and oil, and mix well until smooth.

Divide the batter evenly between the two prepared pans.

Bake for 25-30 minutes or until a toothpick comes out clean from the center of the cakes.

Let the cakes cool in the pans for 10 minutes, then remove from pans and cool completely on a wire rack.

For the frosting: In a bowl, beat together peanut butter, powdered sugar, and butter until smooth. Add milk as needed to achieve a fluffy texture.

For the ganache: In a small saucepan, heat the heavy cream until it just begins to simmer. Pour over the chocolate chips and let it sit for 2 minutes, then stir until smooth. Add the peanut butter and mix until well incorporated.

Assembly:

Place one layer of cake on a serving plate. Spread a generous layer of peanut butter frosting on top.

Place the second cake layer on top and frost the entire cake with peanut butter frosting.

Drizzle the chocolate ganache over the top and sides of the cake. Optionally, garnish with chopped peanuts for a crunchy touch.