Preheat the oven to gas mark 4 or 180°C (350°F)
In a large bowl whisk the flour, caster sugar, baking powder and salt together until well combined
In a jug add the cocoa powder to the boiling water then mix until all of it is dissolved
Add the eggs, oil, buttermilk and vanilla extract to the cocoa mixture then whisk until well combined
Pour the liquid mixture into the flour mixture then mix until just combined
Stir through majority of the chocolate, leaving some chunks to top the muffins, then fold until evenly distributed
Line the muffin tray with case then transfer the batter evenly into each one and top with the remaining chocolate chunks
Bake in the centre of the oven for 15-20 minutes until a toothpick inserted in the centre of the muffin comes out clean
Allow to cool in the tin for 10 minutes then transfer to a wire rack to cool completely before dusting with a sprinkle of icing sugar
Dust with a sprinkle of icing sugar and your chocolate muffins are ready!
