For the roll:
Beat the eggs with the sugar to foam. To them add the sifted flour and vanilla, while stirring carefully with a spatula.
Distribute the mixture in a tray with baking paper. Bake until ready. Then cool and smear with the plum jam.
For the cake dough:
Beat the 3 eggs with the sugar in a deep container. Then add the yoghurt to which you've added the baking powder and stir again.
Sift the flour and add it slowly, a little at a time, to the eggs and yoghurt while stirring nonstop. Lastly add the cocoa while stirring to obtain a homogeneous mixture.
Assembling the cake:
Lay out baking paper in a rectangular form. Place the roll in the middle and on top of it carefully pour on the cake mixture. Bake until ready.
Check it occasionally with a toothpick. Leave it to cool and then cut it. Optionally, sprinkle with powdered sugar.