- Preheat oven to 180 deg C. Prepare one 6" round cake tin. Do not grease.
- Mix both butter consistency into the mixing bowl and add sugar. Cream both till pale and smooth.
- Add yolks to mixture and beat well.
- Gently fold in flour to mixture.
- In a clean and dry bowl, whisk egg whites till stiff. Add cream of tartar and whisk till mixed well.
- Melt chocolate and set aside.
- Take 1/3 whites and mix well into batter. Gently fold in another 1/3 whites into batter and repeat for balance 1/3 whites.
- Pour cake batter into cake tin.
- Pour melted chocolate into cake batter to create swirls.
- Drop tin 2x from 10cm height to release trapped air bubbles and allow chocolate to sink into cake batter.
- Bake for 40-45 minutes at 180deg C.
- Remove from oven and drop tin onto table to prevent cake from shrinking.
- Overturn onto cooling rack to cool completely.