Step by step

1. Add the butter and 400 g of caster sugar to the bowl of the stand mixer fitted with Flat Beater. Beat on speed 6 for 3 minutes until fluffy.

2. Lower the speed to 2 and add the eggs, one at a time. Add the flour, baking powder, salt, vanilla and milk. Mix on speed 2 until well combined.

3. Divide the batter in between two bowls.

4. Put 50 g of the caster sugar, cocoa powder and water in a medium bowl and whisk until combined. Add it to one of the bowls with the batter and mix on speed 1 until combined.

5. Dollop some of the vanilla batter into a prepared pan and spread it out over the bottom. Using another spoon, dollop some of the chocolate batter over the layer of vanilla batter. Push the chocolate batter down slightly, leaving some of the vanilla batter visible. Repeat these steps until the cake tin is 3/4 full.

6. Bake for 50 minutes in a 175ºC preheated oven.