Preheat oven at 180 deg C. Line 10 x 10 inch baking tray with parchment paper.

In a large bowl, mix egg yolks, vanilla extract, sugar, cooking oil and fresh milk together with a hand whisk, mix well and add in sifted flour, mix well again. Divide egg yolk batter into two portions and blend the cocoa paste into one of the egg yolk batter.

Meringue - Whisk egg whites to foamy and add sugar in 3-4 batches, continue to whisk egg white to glossy and peaks form.

Gently fold half of the meringue to the egg yolk batter and cocoa batter with a rubber spatula.

Pour the plain batter on lined pan. Then gently pour cocoa batter on top of the plain batter and spread evenly with a spatula.

Draw lines closely for the entire pan top and down. to and fro (with a ladle handle or use your index finger), then repeat the lines vertically.

Bake in preheated oven 180 deg for about 15 to 17 minutes.

Remove baking baking paper immediately after baked and leave cake to cool on wire rack with a clean parchment paper below (chocolate side at the bottom).

Trim off the sides of the cake and spread filling, then roll up the cake and chill in the refrigerator for a few hours before slicing.