Place the cream, milk, lemon rind and cinnamon stick in a saucepan and bring to the boil. Remove from the heat and leave to infuse for 30 minutes. Beat together the egg yolks and sugar in a bowl, then gradually whisk in the warm cream mixture.
Put 6 ramekins in a deep roasting tin and pour in boiling water to come halfway up the sides of the ramekins. Pass the custard through a fine sieve into a measuring jug, discarding the cinnamon and lemon rind, then pour into the ramekins. Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 30 minutes until just set with a slight wobble in the centres. Remove from the tin and leave to cool completely in the refrigerator.
When ready to serve, sprinkle over enough sugar to cover the tops of the custards. Caramelize the tops using a blowtorch or place under a preheated hot grill for 1–2 minutes until the sugar browns and melts.