Adjust oven rack to lower-middle position and heat oven to 500 degrees.

Line a lipped cookie sheet with parchment paper and trace two side-by-side rectangles. Crumple paper, smooth out again and line the bottom of the pan.

Whisk together confectioner's sugar, granulated sugar and cornstarch. Set aside.

In the mixer bowl, beat egg whites and cream of tartar until foamy and white. Gradually add sugar mixture while mixing on low speed. Increase speed to medium-high and beat to marshmallow cream consistency (2 to 3 minutes).

Flick water onto parchment paper, divide meringue in half, spooning mounds onto rectangles. Smooth out with spatula.

Set meringues in oven. Turn oven off but leave light on. Let meringues dry overnight. Remove from oven and invert. Peel off parchment. Wrap in foil and set aside.

Whip cream to soft peaks, add remaining sugar and vanilla. Arrange first meringue on a platter, spread with half whipped cream and sprinkle half raspberries. Repeat for second meringue with remaining ingredients.