1. Cut a piece of parchment paper to cover the bottom and sides of the jelly-roll pan.
2. Sift flour and corn starch into a medium bowl and set aside. Pre-heat the oven to 190C degree.
3. Beat eggs with sugar in a medium bowl until creamy (about 3 mins) with an electric hand mixer.
4. Add vanilla and mix well.
5. Add all the flour mixture and mix gently using spatula (do not overmix the dough).
6. Pour the batter into the prepared sheet pan, Flatten the surface with the spatula. Tap gently the bottom of the pan to punch out the air.
7. Bake for about 10-12 minutes or until a cake tester inserted in the middle comes out clean.
8. Remove from the oven, immediately loosen the edges of the cake from the pan gently. Flip the cake upside down. Peel off the parchment paper you just used for baking (i actually use usual paper sheets for printing). Let the cake cool completely.
9. Add heavy cream in a bowl and whip until firm-peak. Melt chocolate in microwave for about 1 min (do not overcook) or until smooth no chocolate lumps. Slowly add melted chocolate into whipped cream.
10. Spread the chocolate whipped cream over the rougher side of the cake, spreading the cream at the far end thinner than the front.
11. Roll the cake, together with the parchment paper, then tighten the paper to firm it up. Wrap the paper firmly around the cake and leave it for a while. Refrigerate a few hours to set.