Dissolve the instant espresso powder in hot water and set aside to cool slightly.

Melt the dark chocolate in a heatproof bowl set over a pan of simmering water, stirring until smooth. Remove from heat and let cool for 5 minutes.

Stir the espresso mixture into the melted chocolate until well combined, then whisk in the egg yolks one at a time.

In a clean bowl, whip 200ml of the double cream with vanilla extract until soft peaks form, then gently fold into the chocolate mixture.

In another clean bowl, whisk the egg whites with a pinch of salt until foamy, then gradually add the caster sugar and beat until stiff glossy peaks form.

Fold one-third of the egg whites into the chocolate mixture to lighten it, then gently fold in the remaining whites until no streaks remain.

Divide the mousse evenly among 6 small glass jars or ramekins and refrigerate for at least 4 hours or overnight until set.

Before serving, whip the remaining 100ml double cream with icing sugar until soft peaks form.

Top each mousse jar with a dollop of whipped cream, chocolate shavings, and a fresh raspberry.