Start with the layers. Pour the eggs and sugar in a bowl, beat with a mixer. Then add the flour, cocoa, vanilla, baking powder and water. Beat until homogeneous. If the mixture becomes too thick, add a little more water.
Divide up the resulting mixture into 3 equal parts. Lay out baking paper in a baking form and bake the layers 1 by 1. Bake until ready in a preheated 356°F (180 °C) oven - your toothpick needs to come out dry when poking them.
While the layers are baking you can make the cream. Take the mascarpone and cream cheese out of the fridge so that they're at room temperature. Pour the mascarpone, cream cheese and powdered sugar in a large bowl. Beat until homogeneous. In a separate bowl, beat the confectionery cream with a mixer until it turns to a stiff snow.
Next, gradually add it to the mascarpone and cream cheese, while stirring with a wooden spatula. Leave a little of this cream aside to decorate the sides and top of the cake.
Crumble part of the Oreo cookies. Add them to the prepared cream - quantity as desired. Leave enough biscuits for the decoration though. You can add the rest to the cream.
Once everything is prepared, start assembling the cake. Put the 1st cake layer in a cake form and poke holes in it with a fork. Then syrup it with the sugar that you've dissolved in water. Pour 1/2 the cream on top. Distribute it evenly over the whole layer.
Place the 2nd layer, poke holes again and syrup it. Pour the other 1/2 of the cream and even it out. Place the 3rd layer and syrup it as well. Smear the very top with the set aside cream, smear the cake's sides with it as well. Smooth the cake out well.
Finally, decorate the cake. I decorated mine as follows: I halved part of the remaining cookies. I put the halves without the cream aside and the other halves along the sides of the cake. Then I poured chocolate topping along the edges of the cake, so it poured down the sides. I chopped the remaining cookies in half and put them on top.
Crumble any of the remaining cookies that broke and sprinkle them over the parts of the cake where you can see the cream. Sprinkle chocolate topping at the very top once again. Leave the cake in the fridge overnight, then enjoy its amazing taste.