Crumble all 3 types of chocolate and melt them separately in a water bath with 1 tbsp butter each.
Beat the egg yolks with the powdered sugar in a water bath to a smooth and fluffy cream. Be careful not to cook them.
Divide them into 3 equal parts and stir each one with one of the types of chocolate, after they've cooled slightly.
Separately, beat the cream until fluffy and mix equal parts of it with the 3 types of chocolate.
Lightly grease pyramidal dessert cups.
In each, pour white chocolate mixture, smooth it out, then milk chocolate and finally the dark chocolate one.
Smooth out well and put the cups in the freezer 1-2 hours before serving.