1. Cook lemon juice, zest, egg yolks and ½ cup sugar over double boiler over medium high heat. Stir constantly with a whisk until mixture thickens.
2. Dissolve 1 TBSP plain gelatin in ¼ cup water. Add to egg mixture and stir with whisk. Cool until partially set.
3. While mixture is cooling, beat egg whites at high speed with whisk attachment until stiff peaks form. Add ½ cup sugar and mix for 20-30 seconds, just to incorporate. 
4. With a rubber spatula, gently fold whipped egg whites into lemon mixture until both mixtures are seamlessly incorporated and there are no streaks. 
5. Pour into a cool pie shell and chill in the refrigerator until filling is set (at least 30 minutes).

Garnish with sweetened whipped cream, berries, and/or toasted pecans.