Have ready eight individual serving glasses or a 1.2 litre/2 pint (5 cup) serving dish.

Soak the carrageen moss in a bowl of tepid water for 10 minutes. It will swell and increase in size. Strain off and discard the water and then put the carrageen into a pan with the milk and the vanilla pod, if using. (If using vanilla extract, it will be added later.) Bring the milk slowly to a boil, watching that it doesn’t heat too fast: if the milk heats too quickly, it might suddenly expand in volume and overflow. Reduce the temperature to maintain a very gentle simmer for about 15 minutes, until the carrageen moss has softened and is somewhat dissolved into the milk.

Remove the pan from the heat. Test for a set by placing a teaspoon of the mixture on a saucer. This small amount, when cooled, will show how firm a set the pudding will have. Ideally the mixture should have a soft set; if it is too firm, a little more milk can be added to adjust it. If it does not test for a set, cook for a few more minutes.

At that point and not before, separate the egg. Put the white in a spotlessly clean bowl and set to one side. Put the yolk into a separate bowl with the sugar and vanilla extract, if using, and whisk together for a few seconds. Pour the hot milk and carrageen moss through a fine-mesh sieve into the egg yolk mixture, whisking all the time. By now the carrageen in the strainer will be swollen and exuding jelly, and you will need to press as much of this as possible through the sieve. Use a rubber spatula, scraping any pulp stuck to the outside of the sieve into the egg and milk mixture and whisk to combine. Discard the vanilla pod, if using.

Whisk the egg white to a stiff peak and gently fold it into the top of the milk mixture, allowing it to remain as slightly uneven fluffy peaks. Do not be tempted to over mix, as the egg white should create a distinct layer on top. Divide between the individual serving glasses, or transfer to the serving dish, and place in the refrigerator to set for at least 3 hours or overnight.

To serve

Serve chilled with softly whipped cream, fruit compote, if using, and dark muscovado sugar.

Note:

Dried carrageen moss weighs very little and is tricky to measure accurately: use too little and the milk won’t set; use too much and the pudding will be too firm. The natural gelling strength of carrageen moss can vary. For this reason, it is important to test the pudding for a set as described in the method above.