In a clean saucepan, boil the cider with the remaining 3 tablespoons of sugar until reduced to 1 1/2 cups, about 15 minutes. Sprinkle the remaining 1 teaspoon of gelatin over 1 tablespoon of water and let stand until softened, about 2 minutes. Whisk the gelatin into the cider mixture until dissolved. Transfer the mixture to a pitcher and let cool completely (but don't let the gelatin set), about 30 minutes. Gently pour 2 tablespoons of the cider into each panna cotta over an inverted spoon and refrigerate until set, at least 2 hours. Serve with the Spiced Ginger Cookies.