Preheat your oven to 350°F (175°C). Prepare two 9-inch round cake pans by greasing and flouring them, and place parchment paper circles at the bottom.

In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.

In a separate bowl, whisk together the buttermilk, vegetable oil, eggs, and vanilla extract.

Gradually add the wet ingredients to the dry ingredients, mixing on low speed until just combined.

Slowly pour in the boiling water while mixing on low speed.

Evenly divide the batter between the prepared cake pans. Bake for 30-35 minutes or until a skewer comes out clean.

Let the cakes cool in the pans for 10 minutes before transferring to a wire rack to cool completely.

In a large bowl, beat the softened butter until light and fluffy.

Gradually add the powdered sugar and beat on low speed until combined.

Add the creamy peanut butter and beat until well incorporated.

Pour in the heavy cream and vanilla extract, whisking until smooth.

Add a pinch of salt to enhance the flavor.

Heat the heavy cream over medium heat until it just begins to simmer.

Pour the hot cream over the chocolate chips in a heatproof bowl.

Let it sit for 1 minute, then stir until the chocolate is melted and smooth.

Stir in the butter until melted and fully incorporated.

Level the cakes if needed, and place one cake layer on a serving plate.

Spread a layer of peanut butter filling over the first cake layer.

Place the second cake layer on top, then pour the ganache over the cake.

Decorate with mini peanut butter cups, chopped peanuts, and chocolate shavings.