Preheat the oven to 350° F. Line your cupcake pans with paper liners. Set aside.
In a medium mixing bowl, combine the cake flour, baking powder and salt. Whisk together and set aside.
Add the butter to the bowl of an electric mixer fitted with the paddle attachment. Beat on medium-high speed for 3 minutes, until light and creamy in color. Scrape down the sides of the bowl and beat for one more minute.
Add the sugar to the butter mixture, ¼ cup at a time, beating 1 minute after each addition.
Mix in the eggs one at a time until incorporated. Scrape down the sides of the bowl after each addition.
Add in the peanut butter and stir to combine.
Combine the buttermilk and the vanilla extract in a liquid measuring cup. With the mixer on low speed, add the dry ingredients alternately with the wet ingredients, beginning and ending with the dry ingredients and mixing just until incorporated. Scrape down the sides of the bowl and mix for 15 seconds longer.
Divide the batter between the prepared paper liners, filling each about 2/3 of the way full (you will likely have batter left over after filling 24 wells.I managed to make a full 3 dozen cupcakes) Bake 18-22 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool in the pans 5-10 minutes, then transfer to a cooling rack to cool completely. When cooled, cut the center out of your cupcake and fill with jam (I used grape).