Separate the eggs, setting the egg whites aside. Whisk the yolks in a heatproof bowl.

Place the 200 g sugar and water in a saucepan over medium heat. Stir until the sugar has dissolved, then bring to the boil. Continue to cook until you have a dark caramel (that’s an ‘Oops, I’ve burnt it!’ dark). Then add the cream and vanilla seeds and continue to boil, stirring until smooth.

Pour the mixture slowly over the egg yolks, whisking constantly. Return the mixture to the saucepan and stir over low heat until it thickens and coats the back of a spoon.

Meanwhile, soak the gelatine leaves in a bowl of cold water for 5 minutes, then squeeze to remove the excess water. (If using powdered gelatine, first dissolve it in 30 ml/1 fl oz water.) Add to the saucepam and stir until dissolved. Strain through a sieve, into a bowl, and set aside to cool.

Fit the whisk attachment to an electric stand mixer; whisk the egg whites and extra 50 g sugar to soft peaks.

Whisk the cream to soft peaks, then fold into the egg whites. Gently fold the cooled caramel through the whites.

note

Makes enough for 2 cakes, if you are doing one layer.

This rich, silky mousse will keep in the fridge for up to 3 days.