Method

1. Put the chocolate, porter beer, coffee, sugar & salt in a heatproof bowl over a pan of gently simmering water (don’t let the bowl touch the water). Whisk together until the chocolate has melted & the mixture is smooth.
2. Whisk the egg yolk into the chocolate mixture & then remove the bowl from the heat & set aside to cool. 
3. Whilst the chocolate mixture is cooling down, place the cream & vanilla in a bowl & beat with electric beaters until the cream retains soft peaks. 
4. Gently fold the cooled chocolate mixture into the whipped cream until combined.
5. Divide the mixture between 4-6 glasses or bowls. Chill the mousse in the fridge for a minimum of 2 hours, ideally overnight. 
6. Top with some whipped cream & chocolate shavings.