How to Make It
In a large bowl, sprinkle gelatin over ¼ cup cold water; let stand 10 minutes. Meanwhile, in a small saucepan, combine cranberries and ¼ cup water. Bring to a simmer and cook until berries have burst, about 5 minutes. Puree cranberry mixture until smooth.
Set the vanilla cookies on work surface. In a medium saucepan combine the sugar, corn syrup, vanilla bean seeds, cranberry puree, and ¼ cup water. Bring to boil and cook until the sugar has reached soft ball stage or a candy thermometer clipped to the pan registers 235°F. Beat the reserved gelatin mixer with an electric mixer on medium, then carefully pour the boiling syrup down the side of the bowl, taking care to scrape as much of the cranberry as you can out of the pan. Increase speed to medium-high and beat until mixture is thick, light pink, and cool, about 5 minutes.
Quickly transfer marshmallow fluff to pastry bag fitted with a small round tip. (Or, if you don’t have a pastry bag, use a zippered plastic storage bag) Pipe a small round of marshmallow onto each cookie. Let the cookies stand at room temperature until marshmallow has set, about 2 hours.
In a microwave-safe glass bowl, microwave the chocolate, stopping and stirring every 30 seconds, until it is melted and smooth.
Dip the marshmallow-topped cookies in the melted chocolate so that they are covered completely. Let any excess chocolate run off the cookies, then transfer them to a parchment-lined baking sheet. Chill cookies until the chocolate is set, about 20 minutes.