Step 1

Crust: Preheat oven to 300°F with a rack in center. Lightly brush a 9-inch pie dish with butter. Beat egg whites and cold water on high speed until foamy, about 30 seconds. Add cream of tartar and continue to beat until soft peaks form, about 1 minute. Gradually add sugar and beat until thick, glossy peaks form, about 5 minutes.

Step 2

Spread meringue into an even layer along bottom and up sides of prepared pie dish to form crust. (Don't spread past rim, or it will fall over edges during baking.) Bake until crisp and light golden on outside, 40 to 45 minutes. Turn off oven and let cool in oven 1 hour, then transfer to a wire rack and let cool completely.

Step 3

Filling: Meanwhile, add enough water to lemon juice to yield 1/2 cup (about 2 tablespoons plus 1 teaspoon). Combine gelatin and 1 tablespoon lemon mixture in a small bowl.

Step 4

In a medium saucepan, combine sugar, 2 cups strawberries, and salt. Using a potato masher, gently mash berries. Bring to a boil over high heat, then reduce heat to medium-low and simmer, stirring frequently, until mixture is juicy, about 5 minutes. Whisk cornstarch into remaining lemon mixture; stir into pan with berries and return to a boil.

Step 5

Cook until liquid is very thick and clear, about 1 minute. Stir in gelatin mixture, reduce heat to low, and cook, stirring, until gelatin is fully dissolved, 30 seconds. Remove from heat and let cool 5 minutes. Stir in remaining berries and pour into cooled crust. Refrigerate until set, at least 3 hours or, covered, up to 1 day. Top with whipped cream and whole or halved berries just before serving.