1. Preheat oven to 350 degrees F.
2. Combine all of the cake ingredients and mix with a mixer until combined. Do not over mix, but make sure all dry ingredients and wet ingredients are well combined. Set aside.
3. In a separate bowl, combine peanut butter, butter, powdered sugar, vanilla and salt and mix well with a mixer.
4. Spoon half of cake batter into a bundt cake pan that has been sprayed with non-stick cooking spray. Spoon peanut butter filling on top of the cake batter. Top with remaining cake batter.
5. Bake for 50-55 minutes or until toothpick inserted into cake comes out clean. Remove from oven and allow to cool on a wire rack. Remove from bundt pan and top with powdered sugar or chocolate and peanut butter glaze if desired.