Make the topping: Combine cranberries, granulated sugar, and water in a saucepan. Using the tip of a paring knife, scrape vanilla seeds into pan, and toss in pod. Bring to a gentle simmer, and cook until cranberries are soft but have not burst, about 5 minutes. Let cool. Remove vanilla bean. Topping can be covered and refrigerated for up to 2 days.
Make the pavlova: Preheat oven to 200 degrees. Line a baking sheet with parchment paper. Using an overturned bowl or a cake pan as a guide, trace a 10-inch circle onto parchment. Turn parchment over, marked side down.
Beat egg whites, cornstarch, salt, and vinegar with a mixer on medium speed until foamy. Gradually add superfine sugar. Raise speed to medium-high, and beat until stiff peaks form, about 7 minutes. Reduce speed to medium, and gradually add confectioners' sugar. Raise speed to medium-high, and beat until very stiff, glossy peaks form, about 7 minutes. Beat in vanilla.
Using a rubber spatula or a large spoon, spread meringue into marked 10-inch circle on prepared baking sheet, forming a well in center.
Bake until outside is firm and bottom lifts easily off parchment, about 2 hours. (The inside should still be marshmallow soft.) Leave in a warm place to cool to prevent excessive cracking. When cool, carefully remove from parchment. (Pavlova can be stored in an airtight container for up to 2 days.)
Before serving, whisk cream until soft peaks form. Spread in center of meringue. Spoon topping over cream.