Preheat your oven to 180°C (356°F). Line the base of three 7" cake tins with a circle of parchment paper and spray the sides with oil spray. Or if using 6" cake tins, use four cake pans.
Add the cacao powder, muscovado sugar, coffee, and vanilla to a medium bowl. Add ½ cup boiled water and whisk well until the mixture is smooth. Set aside to cool for 10-15 minutes.
To make the vegan "buttermilk" add the soy milk and apple cider vinegar to a small bowl, stir and allow to sit for 10 minutes.
In a large bowl, whisk together the olive oil and caster sugar for a minute. Add the aquafaba and whisk again. Then add the vegan yogurt and whisk again to combine. Add the vegan buttermilk mixture to the bowl and whisk until mixed. Lastly, add the cooled cocoa mixture and whisk again to combine.
To another bowl, add dry ingredients (flour, baking powder, baking soda, and salt) and whisk together.
Add the dry ingredients to the bowl with the wet ingredients and use a spatula to fold everything together until you have a smooth batter.
Divide the batter into the lined cake pans and bake for 35-40 minutes. Check they are ready by inserting a skewer, it should come out clean. Allow the cakes to cool in the tins for 15-20 minutes and then carefully turn them out onto a cooling rack to cool further. Refrigerate the cakes in an airtight container until ready to use. Chilling the cakes for a few hours makes them easier to work with and decorate.