After watching the video and downloading the recipe for the Mocha cake I noticed that it calls for self-raising flour and baking powder. Would this not lead to a bigger air bubbles in the mixture? Or is this mixture specifically a bit heavier and requires the extra carbon dioxide? I was always under the impression that self-raising flour was just normal flour with a chemical leavener already added.
Self-raising flour does have a bit of chemical leavener added but recipes often add two. For example a recipe using plain flour will add baking powder and baking soda. This is just to make sure that your cake is nice and fluffy like it's meant to be.