Step 1: Pour 2 cups of apple cider into a small saucepan over medium heat. Simmer until the liquid has reduced to 1 cup, then set aside to cool slightly.
Step 2: In a small bowl, sprinkle the gelatin powder over 1/4 cup of the reduced apple cider. Let it sit for 5-10 minutes to bloom.
Step 3: In a separate medium saucepan, combine the heavy cream, sugar, cinnamon stick, and salt. Heat over medium-low, stirring constantly until the sugar is dissolved. Do not let it boil.
Step 4: Remove the cream from the heat. Whisk in the bloomed gelatin mixture until completely dissolved and no lumps remain.
Step 5: Stir in the remaining reduced apple cider and vanilla extract. Remove the cinnamon stick.
Step 6: Pour the mixture through a fine-mesh sieve into a pitcher, then divide evenly among 6 ramekins or dessert glasses.
Step 7: Refrigerate for at least 6 hours, or until completely set and chilled before serving.