Melt the butter and let it cool.

In a bowl, mix the flour, cocoa, and baking powder thoroughly.

Wash the eggs with warm water and dry them. Carefully separate the whites into a clean and dry bowl. Reserve the yolks for another dish within a few days. Add a pinch of salt to the whites and whip with a mixer or a hand whisk until stiff peaks form.

Gradually add the sweetener to the whipped whites while continuing to mix.

Slowly pour the cooled butter into the egg white mixture while mixing.

Gently fold the dry ingredients into the whipped mixture using a spoon or spatula until the mixture is uniform and free of lumps.

Transfer the batter to a small baking dish lined with parchment paper. Bake in a preheated oven at 180°C (356°F) until the cake rises and the surface is dry, about 30-40 minutes. Allow the cake to cool completely in the pan.

Remove from the pan and slice after it has completely cooled.