Crack the 10 eggs into a large mixing bowl.
Beat the eggs with a mixer for a few minutes until they become light, foamy and increased in volume.
In a separate large bowl, combine the flour and baking soda.
Add the sugar to the flour mixture and whisk to distribute it evenly.
Pour in the sunflower oil and stir gently until the dry ingredients are slightly moistened.
Add the milk and whisk well until you get a smooth batter with no visible lumps.
Pour in the kefir and mix thoroughly again to keep the batter smooth and lump free.
Finally, add the beaten eggs to the bowl and mix until everything is fully combined into a very thin, liquid batter.
The batter should be even more liquid than classic crepe batter, so do not worry if it looks runny.
Generously grease a deep baking tray or ovenproof dish with soft butter at room temperature.
Pour the liquid batter into the prepared tray, leaving a little space at the top for it to rise.
Cover the tray tightly with aluminum foil on top and around the edges, making sure the foil does not touch the batter.
Bake in a preheated oven at 200 degrees Celsius for 2 hours, then reduce the temperature to 100 degrees Celsius and continue baking for another 2 hours without opening the oven door. When the time is up, the Black Baba is ready; the surface should be dark and the inside well set with visible pores.
Let the cake cool completely in the pan, then cut into tall slices and serve.