Start making the mousse only after your tart base and caramel are ready to use as you have to pour the mousse into the tart pan as soon as you make it, before it sets.
Begin by blooming the gelatin powder. How to bloom gelatin: Sprinkle the gelatin powder (3 gms) into 30 ml of ice-cold water*. Mix the water instantly and let it set in the fridge for at least 10 minutes.
In a heat-proof bowl, add the chocolate chips (105 gms).
In a saucepan, add the milk (105 gms) and Vimto syrup (30 ml) and bring it to a boil.
Pour the hot milk over the chocolate chips and let it sit for a minute until the chocolate is melted. Then combine them using a hand whisk until the chocolate is completely incorporated into the milk.
While the chocolate mix is still hot, add the bloomed gelatin and whisk it until it’s melted and combined into the mixture. Make sure that the mixture is still hot when you add in the gelatin, or it will not incorporate properly. Blend the mixture with a hand blender to emulsify it properly. You can also do this with a hand whisk if you don’t have a hand blender, but the mixture will not mix as well. Set it aside and let it cool to room temperature.
Meanwhile, whisk the liquid whipping cream (150 ml) in a bowl to semi-stiff peaks*.
Once the chocolate mix has cooled to room temperature, pour it into the whipped cream while gently folding it in. Make sure to do this process slowly to retain the airiness of the whipped cream. You want the mousse to be as light and airy as possible.
Keep folding until no streaks of chocolate are left and everything is well incorporated. Your mousse is ready to go.