Preheat oven to 350 degrees F. Spray 9-inch loaf pan with cooking spray and line with parchment paper.

Combine flour, baking powder, baking soda, and salt in a medium bowl. Combine ⅓ cup granulated sugar and 2 teaspoons cinnamon in a separate bowl.

Combine peanut butter, ⅓ cup granulated sugar, and brown sugar in a large bowl. Beat together until well combined, about 2 minutes. Add eggs, vanilla extract, and buttermilk, mixing until well combined.

Add dry ingredients and mix just until combined. Pour half of batter into prepared loaf pan and sprinkle 4 tablespoons of cinnamon sugar on top in an even layer. Use a butter knife to swirl the cinnamon sugar into the batter.

Pour remaining batter on top and smooth the top into an even layer. Sprinkle remaining cinnamon sugar on top. Bake peanut butter cinnamon bread for 45-55 minutes or until a toothpick inserted in the center comes out clean. Remove from oven and let cool completely.