How to Make It
Preheat oven to 250°F. Line a large baking sheet with parchment paper. Whisk together 1 2/3 cups sugar, cornstarch, and cardamom in a medium bowl. Place egg whites, vinegar, salt, and cream of tartar in the bowl of a stand mixer fitted with the whisk attachment. Beat at medium speed until foamy, about 2 minutes. Beating at medium-high speed, gradually add sugar mixture. Increase speed to high, and beat until stiff, glossy peaks form, 6 to 8 minutes.
Spoon meringue onto prepared baking sheet, and spread into a 16- x 11-inch rectangle. Bake in preheated oven until set and firm, about 2 hours and 30 minutes. Turn off oven, and let pavlova stand in oven until completely cool, about 2 hours. Remove pavlova from oven.
Preheat oven to 425°F. Line a large rimmed baking sheet with parchment paper. Combine grapes, oil, and rosemary sprigs on baking sheet. Bake in preheated oven 15 minutes. Remove from oven, and stir. Add pear wedges to pan; stir gently to combine. Bake until pears are tender, about 12 minutes, stirring gently after 8 minutes. Let fruit cool until barely warm or to room temperature.
Combine cream and remaining 2 tablespoons sugar in a large bowl. Beat with a handheld mixer at high speed until stiff peaks form, about 3 minutes. Fold in crème fraîche. Spoon whipped cream mixture over pavlova. Top with grape mixture, and sprinkle with pomegranate arils. Garnish with rosemary leaves, if desired.