Preheat oven to 425 degrees. Line crust with aluminum foil; leave an overhang and fold over edge. Fill crust with dried beans, pie weights, or uncooked rice. Place crust on a baking sheet; bake until set and lightly golden, about 20 minutes. Remove foil (and beans). Bake without foil, 5 to 10 minutes more; if crust bubbles up, press down gently. Cool.
Reduce oven temperature to 350 degrees. In a large bowl, whisk eggs, sugar, sour cream, and salt; gradually whisk in lemon juice. Pour mixture into crust. Place on a baking sheet; bake until barely set (center of pie will still wiggle slightly), 25 to 35 minutes. Cool completely.
Make topping: Place 2 tablespoons cold water in a small saucepan, and sprinkle with gelatin; let soften about 5 minutes. Heat mixture over very low heat, stirring, until gelatin dissolves. Let cool.
In a large bowl, using an electric mixer, beat cream and sugar until very soft peaks form. While beating, slowly add gelatin mixture, and continue beating until soft peaks form. Using a rubber spatula, spread over cooled pie. Refrigerate until ready to serve, at least 1 hour or, loosely covered, up to 1 day.