
Prepare the dough. In a bowl, beat the eggs with a mixer at maximum power until they double in size, add sugar. You will get a homogeneous light creamy mass. Add sour cream to the eggs, beat. Quench the soda with vinegar, add it to the dough. Gradually add flour, mix the dough thoroughly with "folding" movements from the bottom up. Divide the dough into two parts. Add cocoa to one of them and mix until smooth.

Pour the cake into the pan. Line the bottom of the pan with baking paper or parchment. Grease the bottom and sides with vegetable oil. Place 2 tablespoons of light dough in the center. Pour the same amount of chocolate mixture on top in the middle. Continue making layers until the dough runs out.

Bake the cake. Place the pan in the oven preheated to 180 degrees for about 40 minutes. Check the readiness with a toothpick. It should come out of the center of the cake dry and without crumbs. After baking, take out the cake and leave it to cool. Then cut the cake in half into two flat circles with a sharp knife or special culinary thread.

Prepare the cake cream. Beat the eggs and sugar with a mixer, pour in the milk. Then pour the mixture into a saucepan and bring it to a boil over medium heat, stirring constantly. Then cool. Beat the softened butter with a mixer for about 10-15 seconds, continuing to beat, add the egg-milk mixture, pouring in 1 tablespoon at a time.

Assemble the cake. Spread the cream on the layers and join them together. Smooth the remaining cream over the surface of the cake.