1. Whisk yolks and sugar in large bowl until creamy.
2. 2. Combine 1 litre (4 cups) of the milk, rind and cinnamon in large saucepan; stir over medium heat until mixture just comes to a boil. Remove immediately from heat.
3. 3. Strain milk in large heatproof jug; pour into egg mixture, whisking constantly. Stir reaming milk and cornflour in small jug until smooth; add to egg mixture, stir to combine.
4. 4. Return mixture to pan; stir constantly over heat until mixture boils and thickens.
5. 5. Pour mixture into 26cm heatproof pie dish; cover refrigerate 4 hours or overnight.
6. 6. Just before serving, sprinkle with extra sugar. Grill until sugar is caramelised.