Heat the cream with the milk for each individual layer separately (without bringing them to a boil). Add the corresponding type of chocolate. Once melted, add 1 packet cuajada, dissolved with a little milk into a sludge. Stir for about 3 min. until thickened.
Assemble the cake as follows: put white chocolate mixture at the bottom of a cake form. Leave it to thicken while you prepare the brown chocolate mixture.
Pour it on top of the white one and leave it again, while you prepare the final dark chocolate mixture.
Pour it over the now cooled brown mixture and finish off with the sponge cake layer. Leave the cake in the fridge overnight.
Before serving, invert the cake, putting the sponge cake layer at the bottom as a base.
Note: Cuajada is a Spanish powdered cheese product that speeds up the setting process of chocolate mixtures.