In a mixing bowl, whip the cold heavy cream until half-whipped.

Add the mascarpone cheese and powdered sugar, then mix until the filling becomes firm and smooth.

Fold in the chopped Kinder Bueno bars with a spatula.

Divide the filling into 2 equal parts.

Briefly dip 9 cocoa biscuits in milk and arrange them in the bottom of a small rectangular pan to form the first layer.

Spread over the first half of the filling and smooth it out evenly.

Dip another layer of biscuits briefly in milk and place them over the filling.

Spread over the second half of the filling.

Finish with one more layer of dipped biscuits on top.

Refrigerate for 1–2 hours so the cake firms up.

To make the topping, heat the heavy cream until just before boiling.

Pour the hot cream over the milk chocolate and dark chocolate. Let it sit briefly, then stir until smooth.

Let the topping cool slightly, then pour it over the chilled cake.

Return the cake to the fridge for about 2 more hours, or until fully set.

If desired, drizzle with melted chocolate and decorate with Kinder Bueno pieces before slicing into bars.