Whisk the egg whites, slowly adding the sugar until you have soft peaks.
Melt the chocolate in two separate bowls over a ban marie. Once melted take the bowls off the heat and quickly stir in 2 eggs yolks into each bowl of chocolate.
Evenly split the egg whites and fold a third into each chocolate mixture until combined. Gently fold in the remaining egg whites until combined.
Layer the dark chocolate mousse into the bottom of a serving glass, then top with an even layer of the milk chocolate mousse. Tap the glass on the table to flatten it, and then set in the fridge for 2-3 hours to firm up.
Serve with a dollop of soft whipped cream and chocolate shavings.