Beat the eggs with the sugar to whitening, add the yoghurt, baking powder, oil and flour and whip to a thick pulp. Add the cocoa and lemon zest. Bake in 2 small round trays (pour in 2/3 of the mixture in 1 of the trays) in the oven heated to 356°F (180 °C) with both the upper and lower grills on.
Switch the places of the trays until the layers become ready. It's always a good idea to put in baking paper to facilitate the removal of the layers. Cut the thicker one in half to get a total of 3 layers. Of course, you can buy ready-made ones, but make sure they are dark.
Add them to the mix, and leave a little grated chocolate for sprinkling on top of the cake. Take 1/3 of the mixture and blend it with the blueberry jam.
Atop the first layer, pour the coffee evenly and smear the top with half of the white mixture. Place the second layer. Soak it with the cognac or baileys and smear it with the blueberry mixture.
Place the third layer and coat the whole cake with the remaining white mixture. The goal is to get it colorful on the inside – white, blueberries and white, to contrast with the dark layers.
Decorate as desired, you can add fresh fruit or just grated chocolate or walnuts. The strained yoghurt cake with blueberry jam is served chilled.