Bring the heavy cream to a simmer in a heavy-bottom saucepan over medium heat. Whisk together maple syrup, cornstarch, and egg yolks. Pour about ¾ of the hot cream into the syrup mixture, then pour the syrup mixture into the remaining cream in the saucepan. Heat over medium low heat, stirring constantly, until hot and thickened slightly. Do not let boil. Strain into a large mixing bowl.