Preheat the oven to 180°C or 350°F and prepare a 12 cup muffin tin with liners.
In a bowl mix together the flour, cocoa powder, baking powder, baking soda and salt. Set aside.
To the bowl add the castor sugar, eggs, milk, neutral oil and vanilla extract. Mix well together.
Start adding some of the flour to the wet mixture, and mix it in the batter.
Finally, gently fold in the chocolate chips.
Divide the batter between the 12 muffin liners. Don't worry if the batter reaches the top of the tin.
On top of the batter, place teaspoons of peanut butter. You can either slightly mix it in or keep it as is.
Bake the cupcakes for about 20 minutes or until a cake tester/toothpick comes out clean.
Remove from pan and let cool completely on a wire rack.