Preheat your oven to 350°F (175°C) and grease and flour an 8-inch round cake pan.

In a mixing bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.

In a separate bowl, beat the softened butter and granulated sugar until light and fluffy, about 3-5 minutes.

Add eggs one at a time, mixing well after each addition, then stir in vanilla extract.

Gradually add the dry ingredients to the butter mixture, alternating with buttermilk, mixing until just combined.

Pour the batter into the prepared cake pan and bake for 25-30 minutes, or until a toothpick comes out clean.

Allow the cake to cool completely in the pan before transferring it to a wire rack.

While the cake cools, whip the heavy cream in a mixing bowl until soft peaks form.

In another bowl, combine peanut butter, powdered sugar, and vanilla extract, beating until smooth.

Add softened cream cheese to the peanut butter mixture and mix until well combined.

Gently fold the whipped cream into the peanut butter mixture until fully incorporated.

Once the cake is cooled, slice it in half horizontally to create two layers.

Place one layer on a serving plate and spread half of the peanut butter mousse over it.

Top with the second layer of cake and spread the remaining mousse over the top.

Cover the cake and refrigerate for at least 2 hours to allow the mousse to set.

To make the ganache, heat the heavy cream in a saucepan until it simmers, then remove from heat and add chocolate chips.

Let the mixture sit for a minute, then stir until smooth and glossy.

Pour the ganache over the top of the mousse layer, allowing it to drip down the sides.

Slice and serve the cake, enjoying the delightful combination of flavors.