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1
Preheat oven to 275u00b0F with rack in middle. Lightly butter 3 (8-inch) round cake pans, then dust sides of pans with confectioners sugar, knocking out excess. Line bottom of each pan with a round of parchment paper.
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2
Pulse superfine sugar, brown sugar, and cornstarch in a food processor until well combined.
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3
Stir together vanilla and vinegar in a small bowl.
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4
Beat egg whites with a pinch of salt using an electric mixer at medium speed until they hold soft peaks. Increase speed to medium-high and add sugar mixture 1 tablespoon at a time. After all sugar has been added, beat 1 minute more. Add vinegar mixture, then beat at high speed until meringue is glossy and holds stiff peaks, about 5 minutes. Spoon meringue into pans (about 2 1/2 cups per pan) and smooth tops.
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5
Bake until meringues have a crisp crust and feel dry to the touch, about 1 hour (insides will still be marshmallow-like).
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6
Turn oven off and prop door open slightly with a wooden spoon. Cool meringues in oven 1 hour. (Meringues may sink slightly and crack while cooling.)
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7
Run knife along sides of cake pans and carefully turn meringues out of pans. Carefully peel off parchment (meringues will be fragile and the crust may crack further). Carefully turn right side up.
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8
Toss berries with sugar and let stand at room temperature until ready to use (up to 1 hour).
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9
Beat heavy cream with sour cream using an electric mixer until it just holds soft peaks. Put 1 meringue on a serving plate and spread one third of whipped cream over it. Spoon one third of fruit (with juice) over top. Repeat with remaining meringues, cream, and fruit.
