Mix the custard powder with 3-4 tablespoons of milk until smooth.

Put the remaining milk, sugar, and vanilla extract into a saucepan over medium heat. Stir occasionally and heat until the sugar has dissolved.

Ladle a little of the heated milk into the bowl with the custard powder mixture and whisk together until well combined. Pour the custard mixture into the heating milk and keep whisking. Turn down the heat to low and cook slowly and gently until thickened.

Pour the custard into a clean bowl and cover with a layer of plastic wrap, laying it over the surface of the custard to prevent a skin forming. Place in the refrigerator to cool completely.

When the custard is cold, remove it from the refrigerator. If it is jelled and no longer pourable, use a whisk to break it up until it is a smooth, pourable mixture.

Using a stand or hand mixer, whisk the heavy cream and vodka until stiff peaks form. Whisk in the cooled custard, then pour the mixture into an airtight/freezerproof sealed container. Freeze for at least 6 hours or overnight.

If you don’t include vodka, allow the ice cream to sit at room temperature for 15 minutes to soften before serving.