Preheat the oven to 375°F (190°C). Line a baking sheet with parchment paper, making sure it extends slightly over the edges for easy lifting after baking.
In a clean, dry bowl, beat the egg whites with an electric mixer until soft peaks form. Gradually add the sugar, a little at a time, while continuing to beat until the mixture becomes glossy and holds stiff peaks. This forms a stable meringue that gives the sponge its airy texture.
In a separate bowl, whisk together the egg yolks, cocoa powder, flour, and salt until smooth. The batter should be thick and lump-free.
Gently fold the yolk mixture into the meringue using a rubber spatula. Mix carefully to avoid deflating the whipped egg whites — the batter should remain light and airy.
2️⃣ Bake the Cake
Pour the batter evenly onto the prepared baking sheet and spread it out using an offset spatula. Aim for an even layer about ½ inch thick.
Bake for 8–10 minutes, or until the cake is set, slightly springy to the touch, and pulls away from the edges of the pan. Avoid overbaking, as this can make the sponge dry and difficult to roll.
