Melt butter and chocolate together in a pot over low heat.
Whisk eggs and sugar until fluffy. Pour the chocolate into the egg mixture.
Sift flour, baking powder, salt, and cocoa into the batter.
Pour the batter into a springform pan with parchment paper at the bottom.
Bake at 175 degrees Celsius (347 degrees Fahrenheit) for 20 minutes.
Soak the gelatin in cold water for 10 minutes.
Melt the white chocolate over a water bath, remove from heat, and let cool slightly.
Whisk eggs and egg yolk in a bowl over a water bath until the mixture thickens slightly and becomes completely smooth.
Remove the egg mixture from the heat, squeeze the water from the gelatin, and melt it in the warm egg mixture.
Then pour the melted chocolate into the egg mixture – still stirring until the mixture is fine and smooth.
Whip the cream to a light foam and add it – preferably in 3-4 stages – to the chocolate/egg mixture until the mousse is uniform.
Take your chocolate cake out of the freezer and optionally place cake plastic around the edge of your springform pan.
Pour the chocolate mousse over the base and place in the freezer for 1-2 hours.
Soak the gelatin in cold water for 10 minutes.
Chop the chocolate and melt it over a water bath.
Stir the egg yolks into the chocolate.
Pour ⅓ of the cream into a pot and heat it to the boiling point.
Remove the pot from the heat.
Wring the water from the gelatin, and melt it in the hot cream.
Stir the cream-gelatin mixture into the chocolate mixture a little at a time until the chocolate mixture combines and becomes smooth and glossy.
Stir in salt.
Let the chocolate mixture cool slightly.
Whip the remaining cream into a foam and fold it into the chocolate mixture.
Spread the chocolate mousse on top of the white mousse and place in the freezer for 1-2 hours.
Chop the chocolate and heat it with cream and glucose syrup in a pot over low heat until it is fine and smooth.
Let cool slightly and carefully spread on your frozen cake.
Optionally, decorate with more chocolate on top ?
