Measure then mix the yoghurt and the milk together stirring well.
Empty packet mix into a bowl and pour the yoghurt and milk mix into the bowl. Stir well.
Pour the mixture into a lined slice tray (28x18cm) Bake in a preheated 175*C oven for 20 -25 mins checking with a skewer to see if cooked. Cool in tin and turn out.
Notes
Original recipe Called for 1 cup of yoghurt and 1 cup of milk but the packet mix was bigger than my home brand 340g so I used less of both of these.I sprinkled mini chocolate chips before baking.Goes well in the freezer.You could try with a flavoured yoghurt but remember they are usually sweetened.I used Greek yoghurt and it turned out quite well and not too tart.This cake does not rise as much as it usually would but it still seems a lightish cake, the acids in the yoghurt helps to aerate. It wasn't heavy like I thought it might be.I'm going to try it with a chocolate mix next time.I'm not sure how a mix from scratch would go but I don't see why it wouldn't work nicely as well.