Preheat oven to 180ºC and boil a kettle.
Grease 6 large ramekins or one large dish
Place ramekins in a rectangular cake tin or a casserole dish.
Place butter, lemon zest and sugar into a food processor and blitz on high until butter is pale.
Add lemon juice, flour, egg yolks and milk and mix to a smooth batter.
Whisk egg whites till firm, they shouldn’t be stiff.
Fold the mixtures together.
Divide batter, between the ramekins.
Pour hot water into the dish till the water goes about half way up the sides of the ramekins.
Bake for 45 Minutes.
Remove the ramekins from the water and serve warm.