1. In a blender, combine strawberries, 3/4 cup sugar, and pinch of salt and puree until smooth. Pour into a 9-by-13-inch baking dish. Transfer to freezer and scrape with a fork every 30 minutes until mixture is thick and slushy, 2 hours. Smooth top with a rubber spatula.

2. In a large bowl, using an electric mixer, beat egg whites on high until foamy. With mixer on medium, gradually add 3/4 cup sugar. Increase speed to high and beat until stiff, glossy peaks form, 3 minutes. In another medium bowl, beat cream and vanilla on high until stiff peaks form, 1 to 2 minutes. With rubber spatula, gently fold whipped cream into egg-white mixture. Pour over strawberry mixture and smooth top with rubber spatula. Freeze until firm, about 4 hours (covered, up to 3 days), before cutting into 12 squares.