Preheat the oven to 180°C / Gas Mark 4.
Place the butter and WHITWORTHS CASTER SUGAR in a large bowl and beat for 2-3 minutes until light and fluffy.
Add the egg yolks and continue beating for 1 minute.
Stir in the flour, lemon zest and juice. Add the milk until fully combined.
Whisk the egg whites until stiff and fold into the mixture.
Pour the mixture into individual buttered ramekins or a large buttered ovenproof dish and bake for 30-35 minutes, or until just set.
Cool slightly, and dredge with WHITWORTHS ICING SUGAR before serving.