Microwave chocolate in a 1-quart microwave-safe bowl at HIGH 1 1/2 minutes or until melted, stirring twice; stir in brewed coffee. Set chocolate mixture aside.
Bring whipping cream, half-and-half, 1/2 cup sugar, and coffee granules to a boil in a heavy saucepan over medium-high heat, stirring until sugar and coffee dissolve.
Beat yolks and remaining 1/4 cup sugar at high speed with an electric mixer until thick and pale. With mixer at low speed, gradually pour hot cream mixture into yolk mixture; return to saucepan.
Cook over medium heat, stirring constantly, 6 to 8 minutes or until mixture thickens and coats a spoon.
Remove from heat; stir in chocolate mixture. Cover and chill 2 hours.
Pour chilled mixture into freezer container of a 5-quart hand-turned or electric freezer. Freeze according to manufacturer's instructions.
Pack freezer with additional ice and rock salt, and let stand 1 hour.
