In a saucepan, add 1 cup of milk, lemon zest and cinnamon and bring it to boil on meduim low heat.
In a mixing bowl, whisk the corn flour and sugar into the remaining 2 cups of milk till all dissolved and smooth.
Pour slowly into the boiling milk, whisking constantly to avoid lumps.
Cook on low flame, stirring occasionally to avoid sticking to the bottom, till the mixture turns translucent and slightly thickened.
Switch out, fish out the cinnamon stick and zest. Discard them.
Pour into serving cups or a one liter glass pan. Allow to cool completely by loosely wrapping around a cling film and making a small hole for air passage.
Refrigerate for 3 hours or till completely set.
Serve cold with topping of choice.