1. Preheat the oven to 300ºF (150ºC). Place your gratin dishes or ramekins in a deep sided baking dish. Heat water in a saucepan or electric teakettle to use for baking the custards.
2. Warm the cream, milk, 1/3 cup sugar, and vanilla bean seeds (or paste, or ground beans) in a small saucepan over medium heat. In a bowl, stir together the egg yolks. When the cream is warm, remove it from the heat and gradually pour it into the yolks, whisking constantly. Strain the custard through a fine mesh strainer into a large measuring cup with a spout or small pitcher.
3. Pour the custard into the gratin dishes or ramekins, then add hot water to the pan to the baking dish, until it reaches halfway up the outsides of them, aiming carefully so you don’t get any in the custards.
4. Bake the custards until they are just set when you jiggle them. For shallow gratin dishes, mine took 15 to 20 minutes, in ramekins they took 20 to 25 minutes. (In Mardi’s book, she advises 45 to 50 minutes, so they may take longer in your oven.)
5. Remove the cooked custards from the water bath, being careful as they are quite hot, and cool on a wire rack. When cool refrigerate the custards until they are completely chilled. (They can be refrigerated 3 to 4 days if you wish. Cover them in the refrigerator to prevent them from picking up other odors, if you do.)
6. To caramelize the custards, sprinkle each custard with enough sugar to cover the top. My gratin dishes took about 1 tablespoon of sugar each; ramekins may take slightly less. Use a blowtorch to caramelize each custard.
The best way to do this is to wave the blowtorch over the top until the sugar starts to melt and bubble. Then, carefully, tilt the dish with one hand while you wave the flame over the custard, turning it so that the caramel covers the top in a relatively even layer and doesn’t burn. You may want to wear an oven mitt for holding the custard dish if you are worried about spills. Let them caramel harden and serve.