This featherweight, sweet cake is offset by a tart sorbet. Fresh raspberries mixed into the batter give this dessert a hint of pink.
Preheat oven to 350 degrees, with rack in lower third. Cut parchment to fit bottom of round or heart-shaped 10-inch tube pan with legs or removable bottom. Fit paper into pan. Do not grease pan.
Sift flour, 1/2 cup sugar, and salt together. Sift again into a bowl. Using fork, mash 1/2 cup whole raspberries; strain through a fine sieve to yield about 1/4 cup mashed raspberries.
In the bowl of an electric mixer fitted with the whisk attachment, beat egg whites on medium-low speed until foamy. Beat in cream of tartar and vanilla. Increase speed to medium-high; beat until whites are nearly stiff. Reduce speed to medium-low; beat in the remaining 1 cup sugar, 2 tablespoons at a time. Beat until peaks are almost stiff but not at all dry. Transfer egg whites to large bowl.
Sift flour mixture over egg whites; fold in gently with large rubber spatula. Gently transfer 1/3 of batter to tube pan. Spoon 2 tablespoons mashed berries over egg whites. Spoon another 1/3 of batter into the pan; repeat with remaining mashed berries. Top with remaining batter. Run a knife through mixture, touching bottom of pan, to eliminate any air pockets. Leave the top very textured with peaks in the meringue; do not smooth.
Bake until the top of the cake is lightly golden and the cake springs back when pressed lightly, 35 to 45 minutes. (If top darkens too quickly, tent with foil.)
Invert pan onto its legs or hang it over the neck of a bottle or funnel; let cake stand, in the pan, until completely cool, about 1 hour. Run a knife around edges of the cake to loosen the sides. Unmold cake. Serve with buttermilk sorbet and remaining whole raspberries.