Chocolate sponge cake for cake

1.Separate the whites from the yolks.
2.Whisk the whites with sugar until a fluffy foam forms.
3. Add soda and citric acid to the yolks, mix thoroughly (the yolks should increase in volume)
4. Combine the whites with the yolks.
5. Add cocoa to the flour and gently mix all the ingredients. Put it in a form (preferably rectangular), covered with parchment.
Bake the dough in a preheated oven (180 degrees) for 30-35 minutes.
Check the readiness of the biscuit with a toothpick.
Cool. Soak the finished sponge cake with syrup and spread with cream (to taste).
You can increase the proportions for a large cake.You can not use cocoa in the dough.