Preheat your oven to 170°C (340°F) on fan/convection mode. If your oven lacks a fan setting, adjust the temperature slightly (see Note 1). Line an 18x13 inch half-sheet baking tray, ensuring the two long edges remain unlined.

In a mixing bowl, whisk together the flour, cornstarch, cocoa powder, salt, and baking powder. Set aside.

In a small bowl, stir the milk, vegetable oil, and instant coffee powder until well mixed. Keep this aside.

Separate the egg whites and yolks carefully. Ensure no yolk contaminates the whites.

In a large mixing bowl, combine the warm water and ⅓ cup (66 g) sugar designated for the yolk mixture. Stir to moisten the sugar. Add the egg yolks and vanilla. Using a hand or stand mixer on medium speed, whip the mixture until it thickens and becomes pale. The ribbons formed should linger briefly before dissolving, taking approximately 5 minutes. Set aside.

In another bowl, whip the egg whites with clean beaters until frothy, about 30 seconds. Gradually add the ⅔ cup (133 g) sugar for the whites, beating continuously. Whip until soft peaks form be cautious not to overwhip. This should take roughly 7 minutes, but keep an eye on it.

Gently fold half of the whipped egg whites into the yolk mixture using a spatula, taking care not to deflate the batter. Sift the dry ingredients into the bowl and fold gently until just combined. Add the remaining egg whites, folding delicately.

Pour in the milk, oil, and coffee mixture, folding until the batter is smooth and flows slightly. If it feels too thick, fold a bit more.

Evenly spread the batter into the prepared baking tray. Smooth the top with an offset spatula, tap the tray to release air bubbles, and bake for 18 minutes. The cake is ready when it springs back gently after being touched. Let it cool in the pan for 15 minutes.

Meanwhile, prepare parchment paper slightly larger than the cake, lightly greasing it with a thin layer of vegetable oil.

Once the cake has cooled, loosen the edges with a knife and invert the sponge onto the greased parchment. Roll it up gently while warm and set it aside to cool completely.

While the sponge cools, prepare the ganache. Combine the chocolate and cream in a microwave-safe bowl. Heat in short intervals, stirring frequently until smooth and fully melted. Avoid overheating the cream. Let it cool and thicken, placing it in the fridge to speed up the process if necessary.

Shortly before assembling the cake, whip the cream. In a large bowl, combine the cream, powdered sugar, and vanilla. Whisk on medium speed until stiff peaks form. Be careful not to overwhip.

Carefully unroll the cooled sponge. Trim the short edges diagonally with a serrated knife for a clean finish.

Spread half of the cooled ganache evenly across the surface. Follow with a layer of whipped cream, leaving a small gap at one end to prevent overflow.

Begin rolling the cake from the opposite end of the gap, creating a tight initial roll. Use the parchment paper to guide the sponge into a compact roll without squeezing out the cream.

Place the roll on a wire rack set over a tray. Remove the parchment paper.

Pour the remaining ganache over the cake, using a spatula to spread it smoothly. If the ganache thickens too much, gently reheat it to a spreadable consistency.

Chill the assembled roll in the fridge for 1 hour to set. Before serving, trim both ends for a clean presentation. Transfer to a platter, slice, and enjoy this decadent dessert!