Sift all of the dry ingredients into a large bowl.
Add the wet ingredients to the bowl and mix until combined.
In a separate bowl, combine all of the peanut butter swirl ingredients until thoroughly combined. Add half of the mixture into the muffin batter and fold in but don't completely mix in.
Scoop and distribute the muffin batter into 12 lined muffin moulds. Spoon remaining peanut butter mixture on top of muffins. Use a blunt knife to roughly swirl the peanut butter into the top of the muffins.
Bake muffins in the oven for 25-28 minutes or until a skewer can be inserted into a muffin and it comes out clean.
Rest muffins for 5 minutes and enjoy! Muffins can be kept at room temperature in an airtight container for up to 3 days. Alternatively, freeze the muffins in an airtight container for up to a month.
If you can eat gluten, substitute both flours for 1 ½ cups plain flour.