Bring the milk almost to a boil in a saucepan over medium heat.
Remove from the heat and set aside.
In a separate bowl, use an electric beater to beat the lemon zest, eggs, sugar and vanilla extract (or paste) in a bowl until pale and creamy.
Stir the cornflour into the egg mixture.
Whisk through the milk.
Pour the mixture into a clean saucepan and whisk over a low heat for 5-8 minutes or until the mixture starts to boil.
Continue to whisk for 2-3 minutes or until the custard has thickened slightly.
Pour the mixture into a bowl and cover the top with plastic wrap (to stop the custard from forming a skin).
Place into the fridge for at least 30 minutes to cool and thicken.
Spoon the cooled custard into the pastry shells and top with fresh raspberries and icing sugar.