Step 1 - Preheat oven to 160C/320F fan forced. Line a giant muffin tin with giant liners (or make your own with parchment, see above). In a large bowl whisk the flour, sugar, cocoa powder, baking powder and salt together until well distributed.
Step 2 -In a jug whisk the yogurt or sour cream, carbonated beverage, oil, coffee powder, eggs and vanilla until smooth. Make a well in the centre of the dry ingredients and slowly add in the wet mixture stirring with a spatula slowly to ensure that there are no lumps (but try not to overmix the batter as it can produce tough muffins as the gluten is overworked). Stir in the chocolate chunks but reserve a small handful for decorating on top. Scoop into the muffin liners (I use a spring loaded ice cream scoop) dividing equally among all 6 muffins. Bake for 30-33 minutes or until the centre springs back.
Step 3 - While the muffins are baking make the chocolate ganache to give it time to cool down and thicken. Place the chocolate chips in a bowl and heat the cream up until boiling. Pour the cream all over the chocolate chips and then cover with a plate and let rest for 7-8 minutes. Remove the plate and stir until smooth and no lumps remain.
Step 4 - With the fatter end of a chopstick make a deep hole in the muffin and spoon the chocolate ganache into the hole and in the centre of the muffin.
