1. Preheat the oven to 350 degrees. Use a fine-mesh sieve to sift together flour and 3/4 cup superfine sugar 4 times.

2. In the bowl of a standing mixer fitted with a whisk attachment, beat together egg whites, water, food coloring, and 3/4 cup sugar on medium speed until foamy. Add salt, cream of tartar, and 2 teaspoons vanilla; whisk until meringue is stiff but not dry.

3. Transfer meringue to a large bowl. In six additions, sift flour mixture on top, folding in quickly but gently.

4. Transfer batter to an ungreased 10-inch tube pan with removable bottom. Smooth top with an offset spatula. Run a knife through batter to release air bubbles. Bake until golden brown and springy to the touch, 35 to 40 minutes.

5. Invert pan on its legs or over the neck of a glass bottle, and let cool completely, about 1 hour.

6. Meanwhile, combine the berries, lemon juice, and remaining 1/4 cup superfine sugar in a small nonreactive bowl. Set aside to macerate while the cake is cooling, about 1 hour. In a separate bowl, stir together the sour cream, confectioners' sugar, and remaining 1 teaspoon vanilla.

7. Carefully run a long offset spatula or knife around the inner and outer perimeter of the pan to release cake. Invert onto serving platter. Serve with macerated berries and sweetened sour cream.