Whisk the eggs and gradually add sugar in three portions while beating. Place the bowl over warm water, ensuring the eggs do not cook.

Beat until ribbons form and hold their shape for about 5 seconds.

Sift cake flour and cocoa powder into the mixture, then gently fold using a spatula to preserve the airiness. Mix melted butter and vegetable oil with a small portion of the batter, then combine it back into the main batter.

Pour the batter into butter-greased molds and bake in a preheated oven at 170°C for 30 minutes. Let cool completely.