Preheat the oven to 200°C.
Melt 150g of chocolate in a glass bowl over simmering water.
Grease two chefs' rings and place them on a baking sheet.
Blend butter, egg, and flour in a food processor.
Add the milk and blend to create a smooth batter.
Fold in half of the melted chocolate.
Fill the rings with the mixture and sprinkle with orange zest.
Bake for 8 to 10 minutes until the centres are soft.
Remove the rings, dust with cocoa, and place on plates.
Mix remaining chocolate with sugar and boiling water for the sauce.
Whip the cream and fold in the remaining orange zest.
Serve the mousse with chocolate sauce, orange cream, and mint.