In heavy saucepan, combine chopped chocolate and half & half. Cook over medium heat, whisking until the chocolate is melted and mixture is smooth, about 5 minutes.
In medium bowl, combine sugar, cocoa powder and salt. Gradually whisk dry ingredients into the melted chocolate mixture and bring to boil. Reduce heat to medium-low and cook, whisking occasionally.
In a separate medium bowl, whisk egg yolks. Temper the eggs by slowly ladling some of the hot chocolate mixture into the eggs while whisking the eggs vigorously to prevent them from scrambling. Once you've incorporated about half of the chocolate mixture with the eggs, pour the egg mixture back into the pan with the rest of the chocolate mixture, stir to combine. Continue cooking and stirring for 5 minutes, until thick, smooth, and steaming. Remove from heat and stir in heavy cream and vanilla.
Pour the chocolate mixture through a mesh strainer into a bowl to strain out any solids or curds. Let cool to room temperature then freeze for several hours OR churn in an ice cream maker according to the manufacturer's directions. (I have a Krups ice cream machine, and it took about 35 minutes.)
If you like soft serve, eat it right away. Otherwise transfer to a container and freeze for a couple of hours to firm up. The ice cream may be quite hard when you first take it out of the freezer, so you may want to let it sit a few minutes to soften before trying to scoop.