1/3 cup plus 2 tablespoons (50 grams) unsweetened cocoa powder
1/2 vanilla bean or 1 1/2 teaspoons pure vanilla extract
2 ounces (55 grams) semisweet chocolate, chopped
4 large egg yolks
1/2 cup (100 grams) granulated white sugar
Note: Half and Half cream is a mixture of cream and whole milk and contains 10 ? - 12% butterfat.
In a small saucepan gradually whisk together the half and half and the cocoa powder until it is a smooth paste. Place over medium-high heat and bring the half-and-half cocoa mixture and the vanilla bean (if using) to the scalding point (the milk begins to foam up). Remove from heat, take out the vanilla bean and scrape the seeds from the bean with the back of a knife, and mix the seeds back into the half-and-half. Add the chopped chocolate and stir until the chocolate has completely melted and is smooth. Meanwhile in a stainless steel bowl beat the egg yolks and sugar until light and fluffy (about two minutes). You can do this with a wire whisk or I like to use a hand mixer. Gradually pour the scalding half-and-half mixture into the whipped egg yolk mixture, making sure you keep whisking constantly so the eggs don't curdle. If any lumps do form, strain the mixture first before heating.
Place the bowl over a saucepan of simmering water and, stirring constantly with a wooden spoon, cook until the custard thickens enough that it coats the back of a spoon (170 degrees F) (77 degrees C). The term 'coat a spoon' is a technique used mainly as a way to test when an egg-based custard or sauce is done. A spoon, usually wooden, is placed in the custard and, when the spoon is raised, the film of custard on the back of the spoon will stay in place even when you draw a line with your finger through the middle of the custard.
Immediately remove the custard from the heat and continue to stir the custard for a few minutes so it does not overcook. At this point stir in the vanilla extract, if using. Cover and let cool to room temperature and then refrigerate the custard until it is completely cold (several hours but preferably overnight).
Transfer the cold custard to the container of your ice cream machine and process according to the manufacturer's instructions. Once made, transfer the ice cream to a chilled container and store in the freezer. If the ice cream becomes too hard place in the refrigerator for about 30 minutes before serving so it can soften.