Briefly dip each ladyfinger into warm milk and arrange them in a single layer in a 20 × 20 cm pan.
In a mixing bowl, whip the cold sweet cream until half-whipped. Add the mascarpone cheese and powdered sugar, then continue mixing until a smooth, firm cream forms. Do not overbeat.
Gently fold in the chopped Raffaello balls and shredded coconut using a spatula. Divide the cream into two equal parts.
Spread the first half of the cream evenly over the layer of ladyfingers.
Dip the remaining ladyfingers into warm milk and arrange them over the cream layer.
Spread the second half of the cream on top and smooth the surface. Refrigerate for 1 hour.
For the topping, heat the sweet cream and butter until it just reaches a boil. Pour the hot mixture over the chopped white chocolate and let sit for a few minutes, then stir until smooth and glossy.
Pour the white chocolate topping over the chilled cake and spread evenly.
Refrigerate for an additional 2 hours before slicing and serving.