Pour the mandarin zest syrup and the cream into a small heavy-based saucepan and bring to a simmer over medium heat. Whisk the egg yolks in a bowl and temper in the boiled mandarin and cream mixture. Whisk well to combine, then pour back into the pan and bring to 84°C (183°F). Remove from the heat.
Soak the gelatine in iced water to hydrate. Squeeze the excess water from the gelatine an