Put a pie dish of about 8-inches in diameter in the freezer for at least 20 minutes. Half-fill the sink with cold water. This is just a precaution in case the custard looks as if it's about to split, in which case you should plunge the pan into the water and whisk the custard. I'm not saying it will - with so many egg yolks in the rich cream, it thickens quickly and easily enough - but I always feel better if I've done this.
Put the cream and vanilla bean into a saucepan and bring to the boiling point, but do not let boil. Beat the eggs and sugar together in a bowl, and, still beating, pour the flavored cream over it, bean and all. Rinse and dry the pan and pour the custard mix back in. Cook over medium heat (or low, if you're scared) until the custard thickens, whisking almost constantly: about 10 to 12 minutes should do it. You do not want this to be a good, voluptuous creme, so don't err on the side of runny caution. Remember, you've got your sinkful of cold water to plunge the pan into should it really look as if it's about to split.
When the cream's thick enough, take out the vanilla bean, retrieve the pie dish and pour the creme into the severely chilled container. Leave to cool, then put in the refrigerator until truly cold. Sprinkle with Demerara sugar, spoonful by spoonful, and burn with a blowtorch until you have a blistered tortoiseshell covering on top.
Put back in the refrigerator if you want, but remember to take it out a good 20 minutes before serving. At which stage, put the bowl on the table and, with a large spoon and unchecked greed, crack through the sugary carapace and delve into the satin-velvet, vanilla-speckled cream beneath. No more talking: just eat.
Recipe courtesy Nigella Lawson, 2007