Set the freezer to fast freeze. Combine 4 egg yolks, 1 tablespoon cornflour and 100g (3½oz) caster sugar together in a bowl, mix until smooth.
Heat 450ml (¾pt) milk in a saucepan until almost boiling. Gradually pour the hot milk into the egg mixture, stirring all the time as you do so.
Now return the egg and milk mixture to the rinsed out pan and cook over a low heat stirring constantly until thickened.
Remove from the heat and pour the thickened custard back into a bowl and allow to cool stirring frequently to prevent a skin forming.
When the custard has cooled completely, whip 300ml (½pt) cream in a large mixing bowl until standing in soft peaks. Add the cool custard, 5 pieces stem ginger, chopped ginger and 4 tablespoons ginger syrup. Mix until evenly combined.
Pour into a shallow freezer proof container and chill for at least 2-3 hours before serving.