Directions

1. The night before serving, adjust oven rack to lower-middle position and heat oven to 500 degrees.
2. Line a lipped cookie sheet (approximately 12 by 18 inches) with parchment paper. Trace two side-by-side rectangles - about 5 inches by 12 or 13 inches - on the paper. Crumple the paper, then smooth it out again and line the bottom of the pan.
3. Whisk together confectioner's sugar, 1/2 cup granulated sugar and cornstarch. Set aside.
4. In the bowl of a mixer, beat egg whites and cream of tartar until they turn from foamy to white and beaters just start to leave a trail. On low speed, add sugar mixture, a heaping tablespoon at a time. Increase speed to medium-high and beat to the consistency of marshmallow cream, 2 to 3 minutes longer.
5. Just before forming meringues, flick water onto parchment with fingertips. Divide meringue in half, spooning two or three mounds down each traced rectangle. Use a rubber spatula, or a cake decorator's metal offset spatula, to fill in and even out rectangles.
6. Set meringues in oven, close door and turn oven off (but leave oven light on). Let meringues dry overnight. Remove, then carefully set a wire rack or cookie sheet over meringues. Invert; peel off parchment and turn right side up. (It's OK if edges chip.) Wrap in foil and set aside until ready to proceed.
7. No more than two hours before serving, whip cream to soft peaks, beating in remaining sugar and the vanilla. Set one meringue on a platter. Spread with half the cream and sprinkle on half the berries. Repeat with remaining meringue, cream and berries. Refrigerate, uncovered, until ready to serve.