Partially fill the bottom of a double boiler with water, and bring the water to a boil.
Pour 2 cups of water into the top of the double boiler with the salt.
Place the top of the boiler onto the bottom.
Whisk 1 cup of sugar with the cornstarch in a bowl until all lumps are gone, and whisk the mixture into the water until smooth. Cook, whisking constantly, until the mixture is thickened and translucent.
In a large bowl, beat the egg whites with an electric mixer until they form stiff peaks.
Pour in the hot cornstarch mixture in a slow, steady stream, beating constantly, until the mixture is fluffy and forms peaks. Beat in 1 teaspoon of vanilla extract.
Spread the filling into the baked pie shell in an even layer, and chill in refrigerator.
With an electric mixer, beat the cream with 1 teaspoon of sugar and 1/2 teaspoon of vanilla extract in a large metal bowl until the cream forms soft peaks; frost the pie with decorative swirls and peaks of the whipped cream.
Sprinkle pie with chopped walnuts. Refrigerate until serving time.
