Preheat oven to 250°F. Line a rimmed baking sheet with parchment paper. Draw the outline of a wreath on the parchment paper. Set aside.
With an electric or stand mixer, whisk the egg whites until foamy. Gradually add in the granulated sugar and whisk for an additional 6 to 7 minutes. The mixture should be stiff and shiny.
With the mixer off, add the lemon juice and vanilla extract. Sift the cornstarch into the bowl and turn the mixer back on to whisk for 1-2 minutes.
Transfer the meringue onto prepared baking sheet shaping it into the wreath.
Bake at 250°F for 1 hour and 30 minutes. Turn the oven off and let sit in closed oven overnight.
Sugared Cranberries
Meanwhile, boil together 1/2 cup sugar and 1/2 cup water until the sugar is dissolved. Let cool for 5 minutes and then combine with cranberries in a bowl. Stir to coat. Cover and refrigerate overnight. Drain liquid from bowl.
Add remaining sugar to small bowl. Toss cranberries in the sugar and then place on a plate and let dry for one hour.
Topping
Ina large bowl, gently fold together the whipped cream and mascarpone. Spoon on top of pavlova. Top with sugared cranberries and pomegranate arils. Decorate with fresh rosemary before serving.
Notes
Once the meringue is removed from the oven, you can cover loosely in plastic wrap for up to 2 days.