Preheat the oven to 180°C (350°F). Put the cream, milk, bergamot and mandarin peel in a pan over low heat for at least 1 hour. Whisk the egg yolks and sugar until pale and creamy and then strain in the infused cream.
Pour into a baking tray and bake for 25 minutes or until split. Leave to cool slightly, then purée until smooth. Soften the gelatine leaves in water for 5 minutes. Squeeze out the excess water, add the leaves to the purée and whisk until dissolved.
Pour into a shallow tray and leave to set in the fridge overnight.