Butter the ramekins or large pudding dish and set aside.
Place the soft butter, caster sugar and lemon zest into the bowl of a stand mixer fitted with a paddle attachment and mix on high speed until pale and creamy.
Once creamy add the egg yolks one at a time mixing well in-between each addition.
Next add the lemon juice, milk and flour and mix well before adding each ingredient. Remove the mixture from the machine and set aside.
In another bowl whisk the egg whites until soft peaks form.
Once the whites are whisked fold them through the butter mixture until evenly dispersed and the mixture is light and fluffy.
Pour the mixture into the buttered mould/s leaving a 2-3cm gap at the top, place the pudding/s onto a perforated tray and into a pre-heated oven steam setting 100 °C for 40 minutes.
Once cooked remove from the oven and dust with icing sugar and serve hot with ice cream or cream.