In a medium mixing bowl, whisk together the remaining cup of milk with the cocoa powder and cornstarch. Add the mixture to the heated milk and agave mixture. Raise the heat and bring the mixture to a boil, stirring constantly. Continue to boil and stir for 1 minute. Strain the mixture into a clean bowl and let cool to room temperature. Cover with a piece of plastic wrap and refrigerate until cold, about 6 hours. (To hasten the chilling process put the mixture in the freezer for approximately 1 hour instead.)

Pour the mixture into an ice cream machine and process for 20 – 30 minutes or according to the manufacture’s directions. Place in a covered container and freeze until hard, about 6 hours. The gelato will keep for a week in the freezer, covered.