In a small saucepan, bring the remaining apple juice (½ cup/125 ml), the sugar, lemon juice and cinnamon to a boil. Simmer while stirring for about 2 minutes or until the sugar has completely dissolved. Add the gelatin and continue cooking over low heat, stirring with a whisk until the gelatin has completely dissolved. Skim at this stage if desired. Pour into the prepared pan. Let rest at room temperature for about 8 hours until set.