In a mixing bowl, whisk together the egg yolks and sugar until the mixture is smooth and pale.
In a saucepan, heat the heavy cream and vanilla extract over medium heat until it begins to steam, but not boil.
Slowly pour the hot cream mixture into the egg yolk mixture, whisking constantly to prevent curdling.
Pour the custard into ramekins and place the ramekins in a baking dish. Add hot water to the baking dish until it reaches halfway up the sides of the ramekins.
Bake the custard for 45 minutes or until set. Remove from the oven and let cool to room temperature, then refrigerate for at least 2 hours.
Once chilled, sprinkle a thin layer of sugar over the custards and use a blow torch to caramelize the sugar until golden brown and crisp.
Notes
Make sure not to overbake the custard, as it should be silky smooth. If you don't have a blow torch, you can caramelize the sugar under the broiler in the oven, but keep a close eye on it!