1. Preheat oven to 200 fan (or depending on your oven temperature).
2. In a bowl put your butter, vegetable oil, both sugars and cream together until your mixture is pale, light and fluffy.
3. Crack in your two eggs and add your buttermilk to the mixture and mix to combine everything. Don’t worry at this point if your mixture is looking a little curdled it will be okay once the dry ingredients are added.
4. Sieve in your flour, cocoa powder, baking powder, bicarbonate soda and salt and mix this together until it is just combined making sure you don’t over mix your batter.
5. Add in the majority of your chocolate chunks or chips and fold them through, I like to save a few to put on the top of my muffins later.
6. Split your muffin mixture between 9-12 muffin cases depending on the size of them and finish them off with some of the left over chocolate chunks on top.
7. Bake for five minutes at 200fan, and then turn your oven down to 180fan and bake for another 15 minutes until well risen and a skewer comes out clean. By doing this and adjusting the oven temperature it will help to achieve that bakery style muffin.