2 1/2 cups half & half
1/4 cup cocoa powder (unsweetened)
1 1/2 tablespoons espresso powder
1 cinnamon stick
4 egg yolks
heaping 1/2 cup sugar
2 oz finely chopped dark chocolate
3 tablespoons Kahlúa
Heat the half & half over medium heat until simmering and then add cocoa powder and espresso powder. Cocoa powder will dissolve as mixture heats. Once dissolved, add the cinnamon stick and continue heating until simmering (do not boil). Remove from heat and set aside.
Beat the egg yolks and sugar until well blended and color turns to light yellow. Continue whisking the egg mixture while slowly pouring in the hot half & half. Return to original saucepan and heat over medium low heat, stirring constantly until custard thickens and finger will leave a trace when drawn across the back of a wooden spoon (about 180 °F).
Pour mixture through a chinois to remove any egg lumps and cinnamon stick. Add the chopped chocolate and stir until melted. Finally, add the Kahlúa. Chill the mixture in an ice bath or the refigerator until approximately 40 °F. Prepare according to the directions of your ice cream maker.