1 1/4 cups sugar
2 1/4 cups water
3/4 cup unsweetened Dutch-processed cocoa powder, sifted
4 ounces bittersweet or semisweet chocolate, finely chopped
Pinch of salt
2 tsp minced orange zest
Combine the water and sugar in a 2-quart saucepan and bring to a boil over medium heat to dissolve the sugar.
Add the cocoa powder and stir until it is dissolved and smooth. Remove the pan from the heat and add the chopped chocolate. Stir until it is completely melted.
Strain the mixture into a bowl, and stir in the salt and orange zest. Cover tightly with plastic wrap and cool to room temperature. Chill for several hours or overnight, then process in an ice cream machine according to the manufacturer’s instructions.