Pre-heat the oven to 175 °C. Place a sheet containing water in the bottom of the oven.
Line a spring form pan (20 cm in diameter) with parchment paper, fixing it to the base so that the mixture does not seep out.
Melt the butter, remove from the heat and pour in the chopped chocolate. Stir until it melts.
Beat the eggs, sugar and vanilla extract until fluffy.
Add the rum and pour the mixture into the springform pan.
Bake for 50–60 minutes until the cake has solidified.
Remove from the oven and leave to cool.
Melt the butter, remove from the heat and add the chopped chocolate.
Beat the egg yolks, sugar and vanilla extract.
Add the melted chocolate and stir.
Whisk the egg whites until firm.
Carefully fold the egg white into the mousse, a third at a time.
Whip the cream and carefully fold it into the mousse until the mixture is completely smooth.
Spread the mousse over the cooled chocolate cake. Cover with cling film and freeze for at least 6 hours.
Heat up the cream in a small saucepan. Remove from the heat and add the vanilla extract and chocolate.
Stir until the glaze is completely smooth, and leave to cool.
Remove the cake from the freezer and place on a cake stand.
Pour the glaze onto the middle of the cake and spread it towards the edges so that it oozes over the sides.
Return it to the freezer and bring it out 20-25 minutes before eating.