Weigh the necessary ingredients. Sift the flour, cocoa, and baking powder through a sieve. Melt the butter in the microwave or on the stove, then cool it down.
For the sponge layers, break the eggs into a bowl, add sugar.
Mix until the components are combined. Place over a water bath so that the bottom of the bowl does not touch the liquid below. The water in the pot should simmer slowly. Keep stirring with a whisk until the sugar granules dissolve. This can be easily checked by dipping a finger into the egg mixture and trying to rub it between your fingers. The liquid will be quite warm.
Whisk with a mixer until slow-flowing traces from the whisks remain on the surface. The mass will increase in volume and lighten in color.
Add about a third of the dry ingredients.
Mix at low speed or with a manual whisk. Here you need to act carefully, trying to preserve as many air bubbles as possible. Introduce half of the melted butter.
Then add a third of the flour, the remaining butter, and finally, all the remaining flour. The batter will be quite liquid and very airy.
Grease the bottom of the mold, here 19 cm in diameter, with butter and pour in the batter.
Bake in the oven at 170 ℃ for 45 minutes. Check for readiness with a wooden stick – a toothpick or skewer. Cool and cut into 3 layers of equal thickness.