The king in question here is Henry IV. And his coronation banquet - at which custard tarts were served - took place in 1399. But Henry IV is not the only English monarch with a liking for them. Called 'doucets' in the Middle Ages, they were equally popular at the court of Henry VIII. Henry's daughter, Queen Elizabeth I, who had a famously sweet tooth, also had a great liking for custard in pastry. At her court, custard tarts grew to enormous sizes and had jesters prancing around in the wobbly mix. The mess must have been quite considerable and I shudder to think about the laundry bill!
All things considered, you can't get more English than this. A pastry case filled with egg custard flavoured with vanilla and dusted with nutmeg is a lovely treat to come home to and goes wonderfully with a cup of Earl Grey tea. To my mind, the tart is best served warm, with a little wobble in the centre, but I've also seen small individual tarts taken on picnics and they didn't seem any the worse for having cooled completely.
Baking this tart is blissfully straightforward and requires nothing more than ingredients most people have in their larder. For 250g shortcrust pastry you'll need a 23cm / 9in flan dish.
Roll out your pastry, line the greased dish and chill the whole for half an hour in the refrigerator. Longer won't hurt.
When you're ready to bake, preheat your oven to 190°C (gas 5 / 375°F).
Remove the pastry case from the refrigerator, line with parchment and fill with rice or baking beans. Bake the base blind until golden. This should take approx. 15 minutes. Take the parchment and beans out of the dish after 10 minutes and return the pastry to the oven to crisp the base.
When done, set the pastry case to cool and reduce the oven temperature to 160°C (gas 3 / 325°F)
Mix the milk and double cream in a saucepan. Slit the vanilla pod lengthways and add to the milk and cream. Bring the mixture to a very gentle simmer and infuse for 10 minutes.
Whisk eggs, yolks and sugar together in a bowl, then remove the vanilla pod from the milk and pour the milk through a sieve into the egg mixture. Whisk thoroughly. The mixture will thicken a little.
Pour the custard mix into the pastry case and sprinkle the top with grated nutmeg or cinnamon. Place in the oven and cook until the custard is set. This will take 30-45 minutes, depending on how wobbly you like your custard tart.
Remove from the oven and leave to cool to your liking before serving.