1.Beat egg yolks and sugar in a large bowl with a balloon whisk until creamy.
2.Combine 1 litre (4 cups) of the milk, rind and cinnamon in a large saucepan; stir over a medium heat until mixture just comes to the boil. Remove immediately from the heat.
3.Strain milk into a large jug; pour milk into egg mixture, whisking constantly. Stir remaining milk and cornflour in small jug until smooth; add to egg mixture.
4.Return mixture to pan; stir constantly over heat until mixture boils and thickens.
5.Pour mixture into a 26cm heatproof flan dish; cover and refrigerate for 4 hours or overnight.
6.Just before serving, sprinkle with extra sugar. Grill until sugar is caramelised.
A blow torch can be used to caramelise the sugar. The custard mixture can be made a day ahead. Caramelise the sugar just before serving. Not suitable to freeze. Milk mixture suitable to microwave.Note