The Sponge Cake:

4 large eggs, room temperature
100g (1/2 cup) granulated sugar
30g (1/4 cup) unsweetened cocoa powder, sifted
60g (1/2 cup) all-purpose flour, sifted
1 tsp baking powder
1/4 tsp salt
1 tsp vanilla extract
The Chocolate Filling:

200ml (3/4 cup + 1 tbsp) heavy whipping cream, chilled
2 tbsp powdered sugar
150g (1 cup) semi-sweet chocolate chips
1 tsp instant espresso powder (optional, enhances chocolate flavor)
For the Ganache Topping (Optional but Recommended):

100g (3.5 oz) dark chocolate, chopped
100ml (1/2 cup) heavy cream

Directions

1. Prepare the Cake Pan and Preheat the Oven

To begin with, line a 10×15-inch jelly roll pan with parchment paper. Next, lightly grease the paper with butter or non-stick spray. Then, preheat the oven to 180°C (350°F) to ensure an even bake.

2. Whisk the Eggs and Sugar to Ribbon Stage

In a large bowl, beat the eggs and granulated sugar together using a hand or stand mixer on high speed for about 7–10 minutes, or until the mixture becomes pale, thick, and triples in volume. This aeration is crucial for a soft and pliable sponge.

3. Sift and Fold in Dry Ingredients

In a separate bowl, combine flour, cocoa powder, salt, and baking powder. Sift the mixture over the whipped eggs in two additions. Gently fold using a spatula in a figure-eight motion to maintain the airiness. Add vanilla extract and fold just until incorporated. Do not overmix

4. Bake the Chocolate Sponge

Pour the batter into the prepared pan and level it with an offset spatula. Bake in the center rack for 12–14 minutes or until the cake springs back when touched gently. Do not overbake — a dry sponge will crack when rolled.

5. Roll the Cake While Warm

As soon as the sponge is out of the oven, dust a clean kitchen towel with powdered sugar. Flip the cake onto the towel, peel off the parchment paper, and immediately roll the cake (along with the towel) from the short end. Let it cool completely in this rolled shape to “train” the sponge and prevent breakage later

Prepare the Chocolate Cream Filling

Heat the cream until it simmers. Pour it over the chocolate chips and let sit for 2 minutes. Add espresso powder if using. Stir until smooth. Chill
this ganache for 30 minutes, then whip with powdered sugar to a spreadable consistency

Fill and Re-Roll the Cake

Unroll the cooled sponge carefully. Spread an even layer of the whipped chocolate filling, leaving a 1-inch border at the edge to prevent overflow. Gently roll the cake back into a tight log, this time without the towel.

Wrap in cling film and refrigerate for 1–2 hours to set.