Preheat the oven to 180°C/160°C Fan/Gas Mark 4. Line a muffin tray with the muffin cases.
Sift the flour and Baking Powder into a large bowl, add the sugar and stir the dry ingredients together until combined and make a well in the centre.
In a separate bowl mix together the eggs, Vanilla Extract, melted butter and milk. Pour into the well in the centre of the dry ingredients and gently fold the wet ingredients into the dry ingredients – be careful not to over mix the mixture, about 10 folds of the mixture, there will still be some flour lumps but this helps with the texture of the muffin.
Pour the Milk Chunks into a separate bowl and add a spoonful of flour, toss the Chocolate Chunks in the flour – this stops the chunks from sinking when the muffins are baked. Pour the Chunks into the muffin mixture and gently stir into the mixture.
Half fill each muffin case with the mixture and add a spoonful of peanut butter. Place the rest of the mixture on top of the peanut butter and using a cocktail stick swirl the peanut butter through the mixture. Bake for 20-25 minutes until risen and a skewer inserted into the centre comes out clean. Leave to cool in the tin for 15 minutes and then place on a wire rack to cool completely.