Preheat oven to 325 degrees F. Spray three 8-inch or four 6-inch pans with nonstick spray, line the bottoms with parchment paper and spray again. Set aside.
Sift together the flour, baking powder, salt, and cinnamon. Set aside.
In the bowl of an electric mixer fitted with a paddle attachment, mix together the butter and peanut butter until creamy. Add in the sugar and mix on medium for about 3 minutes.
Decrease the speed to low and add in the vanilla and eggs, one at a time. Stop the mixer and scrape down the sides and bottom of the bowl.
With the mixer on low, add in half of the flour mixture, then stream in the buttermilk and mix until incorporated. Add in the remaining flour and mix until combined.
Evenly divide the batter between the cake pans and bake for about 30 to 35 minutes or until a toothpick inserted in the center of the cakes comes out clean. Cool on a wire rack for 10-15 minutes before removing the cakes from their pans.