1. Pre-heat an oven to 180 degrees Celsius, fan, or equivalent. Boil a full kettle of water. Generously butter a deep 22-centimetre diameter ovenproof dish with a capacity of around 1.5 litres.

2. Put the butter, sugar and zest of the lemons into a food processor and process until well combined, or cream them together with a wooden spoon.

3. Add the egg yolks one at a time, mixing well after each addition.

4. Mix in a tablespoon of flour followed by a glug each of milk and lemon juice. Repeat until all the flour, milk and juice is incorporated.

5. In a separate, spotlessly clean bowl, whisk the egg whites until they form soft peaks when you lift the whisk. Fold the egg whites gently into the cake batter.

6. Pour the mixture into the buttered ovenproof dish and put the dish into a deep roasting tin. Pour hot water into the roasting tin so that it comes about a third of the way up the side of the cake dish. Carefully put the tin with its dish into the oven and bake for around 40-45 minutes, until the top is golden and springs back when pressed gently. Be aware of the hot steam when opening the oven.

7. Leave the pudding to settle for 10 minutes then either eat hot for maximum lightness, or cold – either way with plenty of cream.  Serve dusted with icing sugar.

Variation: To make an orange surprise pudding, replace the lemon juice and zest with the zest of three oranges and zest of one lemon and 100ml of orange juice.