Prepare three 8-inch cake pans with parchment paper circles in the bottom and grease the sides. Preheat oven to 350°F (176°C).

In a large mixing bowl, cream the butter, sugars, and peanut butter together until light in color and fluffy, about 3-4 minutes.

Add sour cream and vanilla extract and mix until well combined.

Add the eggs one at a time, mixing until just combined after each. Scrape down the sides of the bowl as needed.

Combine dry ingredients in a separate bowl, then combine the milk and water in a small measuring cup.

Add half of the dry ingredients to the batter and mix until well combined. Add the milk mixture and mix until well combined. Add the remaining dry ingredients and mix until well combined. Scrape down the sides of the bowl as needed.

Divide the batter evenly between the cake pans and bake for about 21-23 minutes, or until a toothpick comes out with a few crumbs.

Remove the cakes from the oven and allow to cool for about 2-3 minutes, then remove to cooling racks to cool completely.

In a large mixer bowl, beat the butter and peanut butter together until smooth for the frosting.

Slowly add half of the powdered sugar and mix until smooth. Add 5-6 tablespoons of water or milk and mix until smooth.

Slowly add the remaining powdered sugar and mix until smooth. Add additional water or milk, as needed for desired consistency.

To assemble the cake, level the tops of the cakes with a serrated knife. Place the first cake layer on a serving plate.

Spread about 1 cup of frosting into an even layer on top of the first layer.

Add the second layer of cake on top of the frosting, followed by another cup of frosting, and then the final layer of cake.

Frost the outside of the cake and press peanut butter chips into the sides of the cake.

To make the peanut butter ganache, add the peanut butter chips to a medium-sized bowl.

Heat the heavy whipping cream until it begins to boil and pour it over the peanut butter chips. Let sit for 3-5 minutes, then whisk until smooth.

Drizzle the ganache around the edge of the cake and use the remaining frosting to pipe swirls on top. Fill the center with remaining ganache.