Make the chocolate bowls by melting the chocolate in a bowl placed in boiling water.
Blow up some balloons and cover with cooking oil.
Dip the balloon in the melted chocolate (when it has cooled a bit) and stand on baking parchment
Leave to set.
Make the custard using custard powder and milk following the instructions on the packet
Leave to cool.
To make the mousse separate the egg whites and yolks into two bowls.
Melt the butter and whisk with the egg yolks and sugar.
In another bowl mix the whipping cream until it forms peaks. Stir in 2 tablespoons of sugar.
Whisk the egg whites until they form soft peaks. Stir in 1 tablespoon of sugar.
Whisk the cream into the egg yolk mixture.
Fold the egg whites into the cream mixture
Leave in the fridge to set for a couple of hours.
To serve spoon the mousse into the chocolate bowls and add a spoon of custard into the centre.