To make the cake layers

1. Prepare three 8 inch cake pans with parchment paper circles in the bottom and grease the sides. Preheat oven to 350°F (176°C).
2. In a large mixing bowl, cream the butter, sugars and peanut butter together until light in color and fluffy, about 3-4 minutes. Do not skimp on the creaming time.
3. Add sour cream and vanilla extract and mix until well combined.
4. Add the eggs one at a time, mixing until just combined after each. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
5. Combine dry ingredients in a separate bowl, then combine the milk and water in a small measuring cup.
6. Add half of the dry ingredients to the batter and mix until well combined. Add the milk mixture and mix until well combined. Add remaining dry ingredients and mix until well combined. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
7. Divide the batter evenly between the cakes pans and bake for about 21-23 minutes, or until a toothpick comes out with a few crumbs.
8. Remove the cakes from the oven and allow to cool for about 2-3 minutes, then remove to cooling racks to cool completely.

For peanut butter frosting

1. In a large mixer bowl, beat the butter and peanut butter together until smooth.
2. Slowly add half of the powdered sugar and mix until smooth.
3. Add 5-6 tablespoons of water or milk and mix until smooth.
4. Slowly add the remaining powdered sugar and mix until smooth. Add additional water or milk, as needed to get the right frosting consistency.

To assemble the cake

1. To put the cake together, use a large serrated knife to remove the domes from the top of the cakes so that they’re flat. Place the first cake on a serving plate or a cardboard cake round.
2. Spread about 1 cup of frosting into an even layer on top of the cake.
3. Add the second layer of cake on top of the frosting.
4. Add another cup of frosting on top of the cake and spread into an even layer.
5. Top the cake with the remaining layer and frost the outside of the cake. Refer to my tutorial for frosting a smooth cake, if needed.
6. Press peanut butter chips into the sides of the cake.
7. To make the peanut butter ganache, add the peanut butter chips to a medium sized bowl.
8. Heat the heavy whipping cream until it begins to boil.
9. Pour the hot cream over the peanut butter chips and allow to sit for 3-5 minutes, then whisk until smooth.
10. Drizzle the ganache around the edge of the cake.
11. Use the remaining frosting to pipe swirls around the top of the cake (I used Ateco tip 844), then fill in the center with the remaining ganache.