In a medium saucepan, pour in 1.5 cups of the milk, zest from 1 quarter of an orange or lemon and the scraped seeds and empty vanilla pod and infuse by gently simmering for 10 minutes.
Meanwhile, in a mixing bowl, whisk the eggs, sweetener and cornflour together until smooth.
Pour the infused milk in to the bowl, stir and pour back in to the saucepan and on the lowest heat, stir in the figure of 8, scraping the bottom edges of the pan.
It should start to thicken and will take about 4 minutes, but be careful not to curdle the mixture. If the mixture starts to curdle, just place in a blender and whiz until smooth.
Now take off the heat and stir in ⅕ cup of skimmed milk to stop the mixture from cooking further.
Leave to cool and stir in the rum and top with freshly grated nutmeg and chill in the fridge or serve with ice and enjoy yourself!