First, prepare the sherry gelatin: To a medium, heatproof bowl, add ½ cup cold water and 2 tablespoons plus 2 teaspoons gelatin. Stir to hydrate and set aside until it has completely absorbed the liquid, about 5 minutes.
In a small pot over high heat, bring 3 cups water and the sugar to a boil, stirring occasionally until the sugar dissolves. Remove from the heat and add the sherry and the gelatin mixture, stirring to completely dissolve. Divide evenly among twenty 5-ounce ramekins. Transfer to the fridge and chill until the liquid has gelled, at least 2 hours.
Meanwhile, prepare the tres leches gelatin: To a medium, heatproof bowl, add ½ cup cold water and the remaining 2 tablespoons plus 2 teaspoons gelatin. Stir to hydrate and set aside until it has completely absorbed the liquid, about 5 minutes.
To a small pot over medium-high heat, add 2 cups water, the sweetened condensed milk, evaporated milk, and cinnamon stick, and bring to a boil. Remove from the heat and stir in the vanilla and the gelatin mixture. Cool to room temperature, then remove and discard the cinnamon stick and stir in the half-and-half. Retrieve the ramekins from the fridge and carefully divide the milk mixture over the sherry layer. Refrigerate until the second layer is set, at least 2 hours or up to overnight. (If refrigerating longer than 2 hours, cover with plastic wrap.)
To serve, dip the bottom of each ramekin in a bowl of hot water to loosen, then invert onto dessert plates and serve cold.