Preheat your oven to 325 degrees F. Spray each of your three 8-inch or four 6-inch round cake pans with non-stick spray, line the bottoms with parchment paper and spray again. Set aside.

In a medium bowl, whisk together the cake flour, baking powder, cinnamon and salt. Set aside.

In the bowl of an electric mixer, fitted with a paddle attachment, mix together the butter and peanut butter until creamy on medium-high speed. Add the granulated sugar and mix on medium for about 3 minutes. Turn the mixer off and scrape down the sides of the bowl. Mix again for another 30 seconds.

With the mixer on medium speed, add the eggs, one at a time, making sure to mix between each addition. Add the vanilla.

Decrease the speed to low and add 1/3 of the flour mixture to the batter, followed by half of the buttermilk. Repeat additions, finishing with the remaining flour mixture. Mix on low speed until incorporated. Scrape down the sides of the bowl and mix again for another 20 to 30 seconds.

Evenly divide the batter between the three pans, about 18 to 19 ounces of batter in each of the 8-inch pans. 13-14 ounces of batter if you're using the 6-inch pans. Bake the cake layers for 32 to 35 minutes, until a toothpick inserted in the center of the cake comes out with a few moist crumbs on it. Let cool in pans for about 15 minutes before inverting onto wire racks to cool completely. Once cooled completely, wrap in plastic wrap and freeze for at least an hour chilled. Can be stored for up to a week with the plastic wrap and up to a few months with tin foil also wrapped around each layer.

In a microwave safe bowl or over the stove, heat the cream and the chocolate. Stir to create a smooth ganache. Set aside.

In the bowl of an electric mixer fitted with a paddle attachment, cream the butter on medium speed for 2 minutes.

With the mixer on low speed, gradually add the sifted powdered sugar, followed by the vanilla and salt.

With the mixer on medium speed, slowly add the chocolate ganache. Scrape down the sides of the bowl and turn the mixer to medium-high speed and beat the frosting for about 3 to 5 minutes. Once the buttercream is done, be sure to mix it by hand a bit with a spatula or wooden spoon to push out the air pockets.

Place the first cake layer (top side/crumbly side up) on a cake board that has a little frosting on it (which acts like glue to hold the cake in place).

Spread about 1 cup of the frosting over the cake layer. Place the second cake layer on top and add another cup of frosting. Make sure to get eye level with the cake to check that your frosting is spread evenly across each cake layer. 

When you get the final cake layer, place it top side down on the second layer of frosting. Spread a thin coat of frosting around the entire cake to lock in the crumbs. Freeze the cake for 10 minutes to set the crumb coat.

Continue to frost and decorate the cake with the remaining frosting.