Preheat the oven to 250°F, with racks in the center position and the lower third. Line two baking sheets with parchment. With an electric mixer, whisk the egg whites and cream of tartar until cloudy and foamy. On medium-high speed, slowly stream in the sugar, then crank the speed up high and continue to whip until you have stiff, glossy peaks. Sift in the cornstarch, drizzle in the vinegar and vanilla, and whip for a few more seconds to incorporate.
Divide the meringue evenly between the baking sheets, using a silicone spatula or wooden spoon to spread it into two 8-inch rounds. Make a wide, shallow depression in the center of each meringue, which you will later fill with cream and berries.
Bake for 1 hour. Turn off the oven. Leave the pavlovas overnight either in the oven or at cool room temperature.
Prepare yogurt whipped cream, decreasing the cream and yogurt to ¾ cup each, the vanilla to ¼ teaspoon, and the sugar to 1 tablespoon. (The whipped cream may be made several days ahead and refrigerated, tightly covered.) Using an electric mixer with the whisk attachment, whip the cream on medium speed until soft peaks form. Add the yogurt and vanilla, then continue to whip, slowly streaming 2 tablespoons sugar down the sides of the bowl. Continue whipping until the peaks hold when the whisk is lifted. Taste, whipping in up to 1 tablespoon more sugar, if desired.
Carefully slide a wide spatula or two under each meringue shell and transfer to a platter or cake stand. Just before serving, scrape the Yogurt Whipped Cream into each indentation, gently smoothing the top. Top with the blueberries and drizzle lightly with honey. Serve immediately.
You can find Chery Sternman Rule at her award winning blog, 5 Second Rule.
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This recipe comes from Yogurt Culture by Cheryl Sternman Rule.