Preheat the oven to Gas Mark 6 (400F degrees). Grease a regular 12 cup muffin pan with non stick spray or line with muffin liners and set aside (my muffin pan is non-stick and fairly new so I usually just lightly grease the bottom inch or so of each cup, I never find muffins rise as evenly using liners).

In a large bowl, whisk together the two flours, baking powder, bicarb, salt and cocoa powder until evenly mixed. Stir in the chocolate chunks.

In a medium bowl, whisk together the eggs and both sugars until combined. Whisk in the buttermilk, melted butter, milk and vanilla. Gently stir the wet ingredients into the dry ingredients until there are no obvious pockets of flour left. I prefer to use a silicone spatula to scrape around the bowl and gently fold the ingredients together without over-mixing them.

Spoon the batter into the prepared muffin tin, filling each cup almost to the brim.

Bake in the hot oven for 5 minutes (to help the tops rise), before lowering the oven temperature (without opening the oven door) to Gas Mark 5 (375F degrees) and baking for a further 14 minutes or until a toothpick inserted into the centre of the muffin comes out cleanly.

Allow to cool in the tin for a couple of minutes (but no longer - or they will stick) before transferring to a wire rack to fully cool.

Muffins freeze well and can be defrosted / warmed in the microwave (I usually zap them for 30-40 secs on high - when you need chocolate, you need it now!) Otherwise, they can be stored in an airtight container for 3-4 days.