15 egg yolks
100g Chelsea White Sugar
1 vanilla pod, seeds scraped out
60g plain flour
15g cornstarch
15g milk powder
½ tsp baking powder
1 Tbsp condensed milk
125g melted butter
2 Tbsp sifted cocoa powder
5 Tbsp Blueberry jam

Preheat the oven to 180⁰C. Brush a tin (40cm x 20cm or similar size, swiss roll tin) with butter and line with baking paper.
Beat egg yolk, Chelsea White Sugar, vanilla seeds with mixer till pale white.
Add the dry ingredients, mix with a spatula.
Lastly fold in the warm melted butter & condensed milk into the batter.

Remove 10 Tbsp of batter and mix in the cocoa powder. Pour this into a piping bag.

Pour the remaining batter into the tin. Pipe the chocolate batter onto the surface of the cake diagonally from the top left to bottom right side. Take a chopstick (or similar) to make a marble effect on top of the cake. Place in oven and bake for about 25 minutes, till the surface is light golden brown & a skewer inserted in middle comes out clean.

Once the cake is cooked and still hot, immediately turn out onto a sheet of baking paper. Evenly spread the jam over the cake and then roll up from the long edge gently (like a swiss roll). Let it cool down before cutting it.