1
Preheat the oven to 180°C. Whisk the eggs and sugar on high speed for 10 minutes. Sift the flour and cocoa over the egg mixture and fold in with a spatula. Spread the mixture on an 18 cm diameter baking tray lined with baking paper (bottom) and bake for 15 minutes. Remove the baked sponge cake from the baking tray and cool on a wire rack.
2
While the sponge cake is baking, prepare the sponge moistening mixture (heat the milk and dissolve the cocoa in it).
3
While the sponge is cooling, prepare the cream. 250 g sweet cream, whipped and refrigerated. Soak the gelatine in cold water for 5 minutes; mix the mascarpone cheese smoothly with the hazelnut spread. Heat 50 ml of the cream and melt the gelatine in it. Pour it over the cream and mix well with a mixer. Finally, fold in the whipped cream with a spatula.
4
Cut the sponge cake into two discs, trimming the upper one to a diameter of 14 cm (4 cm less than the diameter of the cake). Place the lower, larger sponge cake on the base, moisten it and place it in the ring. Brush it with less than half of the cream and flatten the surface. Place the smaller sponge on top of the cream and moisten it. Spread it with the spread as desired; cover it with the remaining cream, taking care to fill the rim around the sponge first. Smooth the custard and place the cake in the fridge to chill.
5
When the custard has cooled, pour the chocolate icing over it. Bring the cream to the boil and pour it over the milk chocolate. Wait for one minute and mix until smooth; cool slightly and pour over the cake. Return the cake to the fridge and prepare the chocolate for decoration. Melt the dark chocolate with the oil over steam. Pour it into a small piping bag and make a small hole. Draw lines on the milk icing to recreate the pattern of the chocolates.
6
Chill the cake for at least 5 hours. Remove the ring from the cooled cake and decorate as desired.