Line a loaf pan or any other pan with baking paper.
Break the eggs. Separate egg whites in 3 different glass bowls and mix in all the egg yolks together in another bowl. Stir in the cornstarch and sugar with the egg yolks and keep aside.
Boil the milk stirring gently. Place another bowl filled with water on high heat and let it come to a boil. Meanwhile gradually pour the egg yolk mixture into the milk and keep stirring with a whisk. When the milk and yolks has combined well, remove the bowl from the heat and place it in the hot water bowl such that the base of the bowl touches the boiling water. Keep stirring until the mixture thickens. Remove and let cool.
Mix in the Gelatin with 3 tbsps of water in a small bowl and leave to swell. Place the bowl in hot water and keep stirring till it dissolves completely (You can also use a microwave, just microwave for 4 to 5 seconds on low). Mix the dissolved gelatin into the milk-yolk custard and keep aside.
Whip the cream until stiff and fold it gently into the milk-yolk custard. Now divide this custard-cream mixture into 3 portions.
Melt all the 3 types of chocolates separately using a double boiler (You can use a large bowl with water which can accommodate all the 3 chocolate bowls or cups and melt them simultaneously, remember to use 3 different spoons to stir).
First stir in the melted dark chocolate into one portion of the custard-cream mixture. Beat 1 egg white until stiff and fold it into the dark chocolate-custard-cream mixture. Pour the mixture into the prepared pan and smoothen on top. Place the pan in the refrigerator.
Meanwhile, mix the melted white chocolate with the second portion of custard-cream mixture. Beat the second egg white until stiff and fold it into the white chocolate-custard-cream mixture. Pour this on the first layer of mousse and smooth on top. Transfer it back to the refrigerator.
Repeat the same steps with the milkchocolate and layer it on top of the white chocolate. Let it stay in the refrigerator for 5 to 6 hours or overnight or until you serve.
Before serving, Carefully place the prepared serving plate on top of the loaf pan and turn the pan upside down. Lift the pan up and remove the parchment paper. Decorate with chocolate shavings before you serve.