Preheat oven to 170 (fan forced)
Arrange rack into middle of oven
Grease and line 24 cm cake tin (base measurement)
Place butter into TM bowl and mix 40 seconds / 50 / speed 4 (this will loosen up the butter, but not melt it completely which you don’t want to do … if it is completely melted the cake will be heavier).
Insert butterfly, add yoghurt, milk, vanilla or coffee granules and eggs and mix 10 seconds / speed 3
Add sugar, flour, cocoa powder and custard powder … you will see that the bowl is very full so use a spatula or spoon to stir though some of the batter to bring liquid from the bottom to the top before continuing … replace lid and mix 10 seconds / speed 3
Lift lid, stir around the top again and mix 30 seconds / speed 3
Pour batter into cake tin smoothing over the top
TIP: to get all the batter out, remove butterfly scraping off the mix, sit in on the upturned lid, remove as much batter as possible from bowl into cake tin, return butterfly to bowl and spin 2 seconds / speed 5 so that the remaining batter on the butterfly will spin off onto the sides of the bowl allowing you to easily remove the last bits with a flexible spatula
Bake for 1 hour and 10 minutes, or when a skewer inserted into centre comes out clean (NB: the chocolate buttercake takes a little longer to cook than the vanilla one so always check ... usually it is 1 hour and 15 minutes in my oven but test before you remove)
Cool for 15 minutes before removing to a cooling rack to cool completely before icing