Zest orange and lemon into the pan with whole milk along with the cinnamon stick.
Place the pan onto the stove and bring to a boil. When it reaches a boil remove off the heat and let it infuse for 10 minutes.
In the mean time, add egg yolk, cornflour and sugar to a bowl and combine until a paste is formed.
Strain the milk through a fine mesh sieve into the egg mixture and combine.
Add it back into a clean pan and place on the stove on a low-medium heat, continuously stirring until the custard thickens, cook out for 2 minutes.1
Decant straight into you ramekins and surface wrap with cling film to stop a skin forming. Leave to rest at room temperature for 15 minutes before placing into the fridge for a minimum of 4 hours.
When ready to serve, add demerara sugar to the top and swirl until you have evenly coated the top and decant any excess. With a blowtorch, carefully caramelise your sugar and serve immediately.2