Method
1) Cream butter, sugar and vanilla essence together in mixing bowl till smooth.
2) Add in eggs slowly one by one. The best way is to break the eggs (egg yolks) before adding it in to avoid batter splitting.
3) Make sure batter is completely smooth before proceeding to add the next egg.
4) Add in 1/2 of soft flour, baking powder, sodium bicarbonate and salt. Mix together till batter is smooth.
5) Slowly add in milk while continuing to beat the batter.
6) Add in remaining flour and beat till batter is smooth.
7) Divide batter into 2 equal portion. Melt chocolate by placing it on top of hot water (Bain Marie) and add into 1 portion of the batter. Mix till smooth.
8) Brush shortening on the bottom and sides of a 18cm (7") square baking pan. Line the bottom of pan with grease proof paper to prevent the cake from sticking to the bottom.
9) Scoop the batter into the baking pan alternating between the light and the dark batter.
10) Use the batter of a wooden spoon to swirl batter around evenly forming a marble texture.
11) Bake in oven at 175 C (347 F) for 50 to 55 minutes. Insert a toothpick into centre of cake when done. If inserted toothpick comes out clean, your cake is done.
Recipe makes 1 X 18cmX18cm (7"X7") square baking pan..