Preheat the oven to 180°C.

Sponge cake

Whisk the eggs with sugar until a thick, pale yellow foam forms. Pour in the milk (or water) and continue whisking until smooth.

Combine the flour, cocoa powder, and baking powder, then sift into the egg mixture. Gently fold in with a spatula (not a mixer!). Pour the batter onto a baking tray lined with parchment paper—the sponge cake should be thin. Bake for 15 minutes.

After 15 minutes, check for doneness with a toothpick—if it comes out dry, the sponge cake is ready. Remove from the oven and let it cool.

Once cooled, crumble the sponge cake—this can be done by hand or using a food processor.

Kartoshka

While the sponge cake is cooling, beat the butter with a mixer until fluffy and light. Add sweetened room-temperature condensed milk or room-temperature cream (not cold!) and beat a little more. Mix with the sponge cake crumbs until a paste-like consistency is achieved. Add vanilla. For an adult version, mix in a shot of strong alcohol. Taste—add more cocoa and mix well if the flavour isn’t chocolatey enough.

Shape the mixture into kartoshka-style (potato look) pastries (the appearance won’t affect the taste!), place them on a plate, and refrigerate until set.

Before serving, dust with cocoa powder.

You can add “sprouts” made from buttercream, but that’s optional.