Pour the cream into a saucepan, then add the torn basil leaves and stalks. Bring to a simmer over a medium heat, then remove from the heat and leaveto infuse for 5 mins. Discard the basil and re-heat the cream to a simmer.
Remove the cream from the heat and immediately tip in the chocolate. Leave for a few mins to melt, then stir until smooth. Pour the mixture into four serving glasses and chill for at least 1 hr until firm. (This can be done up to a day ahead.)
In a small saucepan, mix the caster sugar and balsamic vinegar with 2 tbsp water and cook over a medium heat, stirring continuously, until the sugar has dissolved and the mixture has reduced by half to a sticky syrup (about 5 mins). Cool before pouring over the strawberries and allow to soak for at least 1 hr.
Spoon the balsamic strawberries over the creams and decorate with basil.