In a mixing bowl combine the flour, cocoa powder, granulated sugar, baking powder, baking soda and salt. Stir together and set aside.

In a larger mixing bowl combine the eggs, buttermilk, vegetable oil, and vanilla extract. Stir to combine.

Gradually mix the dry ingredients into the wet ingredients, mixing just until combined. The batter will be very thick.

Cover the bowl with a towel and allow the batter to rest for 15 minutes. During this time, preheat the oven to 425ºF / 220ºC. For bakery style muffins, line a 12 count muffin pan with 6 muffins liners, meaning you’ll only fill every other muffin well with batter. Fill the liners with 2 tablespoons of batter.

Heat the peanut butter in the microwave until melty. Drop ½ tbsp of peanut butter into each muffin cup. Use a toothpick to swirl. Then add 4-6 tablespoons of batter, covering the peanut butter. Top each muffin with ½ tbsp of peanut butter, swirling with a toothpick.

Place one pan in the center of the oven and bake for 7 minutes at 425ºF / 220ºC, then keep the muffins in the oven, turn the temperature down to 350ºF / 180ºC and bake for 12-14 minutes or until a toothpick inserted in the center comes out clean. Allow the muffins to cool in the pan. Repeat with the remaining batter, bumping the temperature back up to 425ºF / 220ºC.