Preheat the oven to 180 °C. Prepare either two round (22 cm diameter) or square (16 cm) cake tins, or a big lasagne dish. Butter the bottom and then place a piece of wax or baking paper cut to size inside, and butter that too, or spray with baking spray.
Combine the flour, sugar and salt in a big bowl.
Melt the butter in a big microwavable bowl and add the water. Add to the bowl with the flour mixture, stir, and then beat in the eggs.
In the same microwavable bowl, combine the milk, vinegar, bicarb and essence (it will fizz, which is quite exciting) and then add this to the flour mixture.
Divide the batter in two (using the same bowl again), and add cocoa powder to one bowl and stir well.
Pour the batters in alternate rows into the prepared cake tins. Now use the blade of a knife to make a swirly pattern between the two.
Bake for 30–40 minutes. Pierce with a sharp knife to check if it’s cooked – the knife blade should come out clean.
Recipe reproduced with kind permission from Yum Mo by Carina Truyts, published by NB Publishers.