Note: this mousse contains raw eggs!
Melt 100g dark chocolate in a bowl in a bain-marie until smooth, stir in 25g butter until well blended. Repeat this process
in another bowl with 100g white chocolate. When the chocolate mixtures are nearly cool, beat an egg yolk into each one,
together with a tsp vanilla extract. Whisk 2 egg whites until stiff, adding 4 Tbs caster sugar in stages. Fold a spoonful
of egg white into each chocolate mixture first, then gradually add the rest, equally between the two, stirring to mix well
but taking care not to deflate the eggs too much. Spoon the dark chocolate into glass bowls, and top with the white
chocolate mousse. Chill in the refrigerator for several hours and serve decorated with fresh raspberries.