Begin by separating the egg yolks and whites into two bowls.
In a saucepan, combine sugar, lemon juice, lemon zest, and egg yolks. Cook over medium heat, stirring constantly, until the mixture thickens. Remove from heat and dissolve the gelatin in cold water. Add this mixture to the lemon mixture and stir until well combined.
Gradually add the boiling water and salt to the lemon mixture, stirring until smooth.
Place the saucepan in a larger bowl filled with ice water. Stir the mixture until it starts to thicken and resemble the texture of unbeaten egg whites.
In a separate bowl, beat the egg whites until soft peaks form. Gently fold the egg whites into the lemon mixture until no white streaks remain.
Whip the cream until stiff peaks form, and then fold it into the lemon mixture as well.
Pour the luscious lemon chiffon filling into the prepared pie crust. Refrigerate for at least 4 hours, or until the pie is set and chilled.
When you're ready to indulge, garnish your pie with an extra dollop of whipped cream and a sprinkle of lemon zest.