Preheat your oven to 200ºC (400ºF) or gas mark 6. Grease a 1.5-liter ovenproof dish with unsalted butter.

In a mixing bowl, cream together 55 g of unsalted butter and 115 g of sugar until pale and fluffy, about 3-5 minutes. Add the lemon zest.

Separate the egg whites from the yolks. Add the yolks one at a time to the butter-sugar mixture, blending well. Gradually sift in 55 g of self-raising flour until smooth.

Stir in 285 ml of milk and 3 tablespoons of lemon juice until combined. The batter should be pourable.

Beat the egg whites until stiff peaks form, then gently fold into the batter.

Pour the lemon batter into the greased dish. Place the dish in a roasting tin and add boiling water until it reaches one-third up the sides of the dish.

Bake in the preheated oven for 45 minutes until golden with a slight wobble in the center.

Let the pudding sit for a few minutes before serving warm, optionally with whipped cream or vanilla ice cream.