How to make Smetannyk:

For the sponge:

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1. Preheat the oven to 356°F/ 180 °F.
2. The Smetannyk cake is made using 2 different sponges: a light colored one and a dark one. You can prepare these individually (in case you have just one baking tray, for example - simply halve the quantities of each ingredient used and make each batter one at a time), but to keep things simple and speed up the baking time, we'll make one big batch of sponge batter and divide them into 2 baking trays before placing them in the oven.
3. So, to start with, add the sour cream and the butter in a bowl and mix them together until well combined. Then, add in the eggs and the sugar and baking soda and whip everything well, until the sugar has mostly dissolved.
4. Then, mix in the flour until the mixture is homogenous and lump-free. You should get a smooth batter - not too thick (like a yeast dough), but not too thin either.
5. Line your baking trays with parchment paper. Pour half the amount of sponge batter into one of the baking trays/moulds. Add the cocoa powder to the remaining batter in the bowl, and mix well until the color is even, then pour it into the other tray.
6. Place in the oven and bake for 15-35 minutes (baking time varies depending on your oven and the thickness of each sponge cake, so check for doneness regularly using the toothpick method).
7. Once done, take the sponge cakes out of the oven, transfer to a cooling rack and let them cool down fully.

For the cream:

1. While the cakes cool down, add the sugar and the sour cream to a bowl and whisk until the sugar has fully dissolved. Put the cream in the fridge until it's time to assemble the cake.

Assembly:

1. Carefully cut each of the sponge cakes into halves (2 layers each).
2. Spread some cream on the top of one half of the light-colored sponge, then add a colored layer on top, followed by another layer of cream and so on, until you finish with a final layer of cream on top.
3. Don't forget to spread the cream around the sides of the Smetannyk cake, as well!
4. Place the cake in the fridge and leave for 6-8 hours or overnight. This is to allow the cream time to firm up, and soak into the sponge.

Enjoy!