In a bowl, beat the eggs with the sugar until pale.
Add the oil and the flour sifted with cocoa and baking powder. Mix with a wooden spatula until combined and pour into a wide tray lined with baking paper.
Bake the cocoa sponge in a preheated oven at 180 degrees until a toothpick comes out clean, then cool on a rack.
Prepare the syrup by mixing water and sugar, heating until dissolved. In a separate bowl, whip the liquid cream until soft peaks form, then add mascarpone and sifted powdered sugar to make a smooth cream.
Layer the sponge, syrup, and cream alternately until all 3 layers are arranged and cover the cake with cream on all sides. Chill while preparing the glaze.
For the glaze, heat cream and add milk chocolate pieces, stirring until smooth. Pour over the cooled cake and decorate as desired.