Preheat the oven to 180℃. Sift flour with soda. Prepare the glaze. To do this, mix 100 grams of cold sour cream with 30 grams of sugar and beat thoroughly with a mixer. Cover the top of the cake with cream. Melt the chocolate and 50 grams of butter in a water bath, stirring constantly.
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. Pour in the melted butter and stir again. Gradually adding flour, thoroughly mix the dough with “folding” movements from bottom to top. Divide the dough into two parts. Add cocoa into one of them and stir until smooth.
Line the bottom of the pan with baking paper or parchment. Grease the bottom and walls with 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 you run out of dough.
Put the cake to bake. Place the pan in an oven preheated to 180°C for about 40 minutes. Check readiness with a toothpick. It should come out dry and free of crumbs from the center of the pie.
Make stripes of frosting on top of the cake. To do this, after cooling the glaze a little, pour the mixture into a pastry bag or syringe.