For the custard, place the milk, cream, scraped vanilla pod and vanilla essence into a bowl and leave to infuse for five minutes. Whilst the milk infuses, whisk the vanilla seeds with the egg yolks and sugar until the mixture is pale and fluffy, then heat the infused milk and cream for about 5-8 minutes.
Whisk the two mixtures together by adding the warm milk to the egg yolks. Once combined, return to the pan and cook on a low heat until it reaches 85°C. Strain through a fine sieve into a bowl and set aside to cool.
For the meringue, heat the sugar in 50ml cold water until it reaches 121°C (using a sugar thermometer). Once the sugar has dissolved, increase the heat slowly. Meanwhile, whisk up the egg whites in a grease-free bowl until they form medium-to-firm peaks. Trickle the sugar syrup into the egg whites slowly whilst continuing to stir, and whisk with an electric beater until cool.
While the custard is still warm, add the gelatine leaves and stir until completely dissolved. Add this to the melted chocolate and stir until well incorporated. Once the meringue has fully cooled, add it to the chocolate mixture by folding in gently until fully combined. Finally, carefully fold in the lightly whipped cream.