Recipe and method adapted from: http://thedomesticgoddesswannabe.com
250g salted butter, softened at room temperature (use Golden Churn tin type)
4 egg yolks
1 teaspoon vanilla extract
200g self raising flour, sifted
10g cocoa powder
4 egg whites
1. Cream the butter and sugar until the mixture turns light and fluffy.
2. Add the vanilla extract, and beat that into the batter.
3. Add the egg yolks, one at a time, and beat each one into the batter before adding the next.
4. Fold in half the flour. Then all the milk. And the rest of the flour. Mix just until all the flour has been incorporated into the batter.
5. Transfer 1/3 of the batter into a bowl, and add the cocoa powder. The remaining 2/3 of the batter can be set aside.
6. In a clean mixing bowl, whisk the egg whites until foamy.
7. Add the sugar gradually and whisk until stiff peaks form.
8. Add 1/3 of the meringue to the batter with the cocoa. Fold this in.
9. Fold the remaining meringue to the batter without the cocoa powder.
10. Pour the batter without the cocoa in a lined and lightly greased 8″round pan. Place spoonfuls of cocoa batter around the sides and middle of the cake.
11. Use a spatula to make circular motions to create swirls.
12. Bake the cake at 170°C for 35-40 minutes, or until an inserted skewer emerges cleanly.
13. Once baked, cool the cake in the pan for about 20 minutes before transferring it onto a cooling rack to cool completely.