Line the tart ring with sweet pastry and bake blind.
Melt the chocolate, butter and cream in a bowl over boiling water.
In a mixer, whisk the eggs, yolk and sugar on full speed until thick, light and fluffy.
Fold the eggs through the melted chocolate mix very carefully and fill the tart mould to the top.
Cook in a cool oven at 150C/300F/Gas 2 for 10 minutes. Allow to cool completely.
Do not refrigerate. Serve with orange or passion fruit sorbet.