In a medium saucepan, whisk together the 1/2 cup granulated sugar, 3 tablespoons cornstarch, packed 1/2 teaspoon orange zest, 1/2 teaspoon ground cinnamon, and 1/4 teaspoon kosher salt. Rub any clumps of zest into the sugar with your fingertips so it is evenly distributed.
Set the saucepan over medium heat. Slowly whisk in about 1 cup of the 3 cups half-and-half and whisk until smooth, then gradually add the remaining 2 cups, whisking continuously until smooth.
Bring the mixture slowly to a boil, whisking across the bottom and into the corners of the pan, about 10 minutes. As soon as it begins to boil, remove the pan from the heat and stir in the 6 ounces chopped bittersweet chocolate and 1 teaspoon vanilla extract until the chocolate has melted and the pudding is smooth.
Divide the pudding among six serving bowls. Serve warm, or press plastic wrap directly against the surface of each portion and refrigerate until cold. Top with freshly whipped cream and raspberries, if desired.
