Whisk the egg yolks in a large bowl, gradually adding the 2/3 cup sugar. Continue beating until the mixture is creamy and pale yellow. Bring the light cream to a boil in a saucepan and remove from the heat. Gradually pour the cream into the egg yolk mixture, whisking all the while to prevent curdling of the egg yolks.
Melt the bittersweet chocolate in a heavy saucepan and stir until smooth. Pour into the custard mixture and add the cocoa. Whisk to combine well. Return the mixture to the heavy saucepan and cook over medium heat until the custard coats the back of a wooden spoon. Do not boil.
Combine the 2 tablespoons sugar with 2 teaspoons of water in a small saucepan. Cook over medium - high heat until the mixture forms a golden brown caramel. Do not stir the sugar mixture while it cooks, or it may crystallize. Be careful not to burn the caramel. Pour the caramel into the chocolate custard and whisk well to incorporate. Pour the custard into a large bowl and allow to cool to room temperature. Place in the refrigerator for at least 1 hour. Then place in an ice cream maker and process according to the instructions for your machine or freezer model.
Serves 6.
