Preheat the oven to 340F. Butter and flour an 8-inch pan so you prevent the cake from sticking to the bottom or walls.
Measure your ingredients and place them at hand.
Place the eggs, sugar, pinch of salt and vanilla extract in a large bowl. Set your mixer on medium speed and beat for at least 15 minutes or until the eggs get a pale yellow color.
Add the cocoa powder alternating with the flour, little by little. Sift them over the egg mixture and mix well with a wooden spatula after each addition so you won’t get any lumps.
Transfer the batter to the pan.
Bake for 40 minutes, making sure you don’t open the oven door in the first 20 minutes. If the toothpick inserted in the middle comes out clean, you cake is ready. In the opposite case, leave it to bake 5 more minutes.
Leave the choc sponge in the oven for 10 minutes, with the door slightly open. After that, take it off and set aside for 10 more minutes. Remove from the pan and place on a wire rack to cool completely.