Preheat your oven to 180°C (350°F) and line your jelly roll pan with parchment paper, ensuring the paper extends slightly over the edges.

In a large bowl, whisk the egg yolks with 60 grams of the sugar until the mixture is pale, thick, and ribbons form when the whisk is lifted.

In a separate clean bowl, beat the egg whites until soft peaks form, then gradually add the remaining 60 grams of sugar, continuing to beat until stiff, glossy peaks appear.

Gently fold the sifted cocoa powder into the yolk mixture, then carefully fold in the egg whites in three batches to maintain the volume.

Spread the batter evenly into the prepared pan and bake for 10 to 12 minutes, or until the cake springs back when touched lightly.

Immediately turn the cake out onto a clean kitchen towel dusted with cocoa powder, peel off the parchment, and gently roll the cake up with the towel while still warm; let it cool completely in this position.

While the cake cools, melt the bittersweet chocolate with 50 grams of heavy cream to create a smooth ganache, then let it cool until spreadable.

Whip the remaining 100 grams of heavy cream until firm, then fold into the cooled ganache.

Unroll the cooled cake, spread the chocolate cream filling evenly over the surface, and roll the cake back up tightly without the towel.

Drizzle the top with melted milk chocolate and chill for at least one hour before slicing.