1. Whisk egg yolks and castor sugar together until evenly-blended.
2. In a heavy-based pan, heat cream and vanilla to just below boiling point. Pour cream onto egg yolk mixture, whisking all the time.
3. Return to pan and cook, whisking constantly, until custard thickens. Do not boil. If custard starts to become lumpy, quickly take off the heat and whisk briskly until smooth.
4. Strain mixture into a jug to remove bits off cooked egg. Pour into individual oven-proof bowls.
5. Cover with cling wrap and refrigerate overnight. This is an essential step.
6. An hour before serving, sprinkle tops with an even layer of sifted castor sugar. Place under hot grill until sugar melts and caramelises (watch carefully as it burns easily).
7. Chill for about 2 hours until caramel is set hard. Do not refrigerate for too long as the top will go soggy. Serve at room temperature.
1. If you have a blowtorch, use it to caramelise the topping, rather than grilling.
2. Do not overcook the custard and also make sure that it cooks evenly.