Step 1To make the ice cream base, in a 3-quart non-reactive saucepan, whisk the egg yolks, sugar, salt and milk over low heat and stir gently until warm, about 5 minutes. Increase to medium-low and stir until custard is slightly thickened and steaming hot, about 5 minutes more. Strain through a fine-mesh sieve into a large bowl, scraping the pot as best you can (leave the sieve in place).
Step 1To make the chocolate paste, whisk the sugar and cocoa together in the same pot, then add the chopped chocolate and cream. Bring to a boil over medium heat, whisking constantly until the sugar has fully dissolved and the mixture is bubbling hot. Strain into the ice cream base, then stir in the vanilla extract and crème de cacao. Cool to room temperature (using an ice bath, if you prefer) and refrigerate until cold and thick, at least 4 hours, or up to 1 week.
Step 2Churn according to the manufacturer’s directions until the ice cream is creamy and thick. If your machine has an open top, cover with an inverted cake pan to keep it cold as it churns. Meanwhile, place a flexible spatula and quart container (an empty yogurt tub works great) in the freezer.
Step 3Enjoy freshly churned ice cream as “soft serve,” or scrape it into the chilled container. Press a sheet of plastic against the ice cream to minimize risk of freezer burn, and seal the container. Freeze until firm enough to scoop, about 12 hours, or up to 3 weeks.