Preheat the oven to 180°C and line a 23cm square cake tin or similar.
Combine the flour, coconut sugar, cocoa, baking soda and a pinch of salt in a large bowl and whisk well.
In a separate bowl whisk together the water, vanilla, vinegar and oil, then pour the liquid ingredients into the dry and whisk until smooth and dark.
Pour mixture into the lined cake tin and bake for about 30-35 minutes or until a skewer inserted into the middle comes out clean. Allow to cool before icing.
Either serve dusted with icing sugar and decorated with fresh fruit and marshmallows or make a fluffy (but not dairy free) chocolate icing. Melt dark chocolate in the microwave for 30 seconds at a time, stirring in between, until smooth (or use a double boiler).
Cool to room temperature then whisk in enough yoghurt for desired consistency. Ice cake and decorate with toppings of your choice.