Directions

1. Preheat oven to 350 degrees. Boil juice in a small saucepan over medium-high heat until it has reduced to about 1 cup, 18 to 20 minutes. Remove from heat; set aside.
2. Pulse cookies, 1 tablespoon lemon zest, and 1/4 cup sugar in a food processor until thoroughly combined. With processor running, add melted butter; process until combined. Press cookie mixture evenly into bottom, up sides, and onto rim of a 10-inch pie plate. Bake until golden brown, about 15 minutes. Transfer to a wire rack to cool completely.
3. Put lemon juice into a small bowl. Sprinkle with gelatin. Let soften 10 minutes. Meanwhile, whisk together yolks, 1/2 cup sugar, the juice reduction, and the remaining 2 teaspoons zest in a medium saucepan. Cook over medium-low heat, stirring constantly, until thickened, about 10 minutes (do not let boil). Remove from heat. Add gelatin mixture, and whisk until gelatin has dissolved completely.

   

4. Transfer gelatin-egg yolk mixture to a large bowl. Refrigerate, stirring occasionally, until cool and thick enough to hold a ribbon on surface, 25 to 30 minutes.

   

5. Put egg whites and cream of tartar into the bowl of an electric mixer fitted with the whisk attachment; beat on medium-high speed until soft peaks form. Gradually add remaining 1/4 cup sugar; beat until stiff but not dry peaks form. Fold egg-white mixture into gelatin-egg yolk mixture in 3 batches, folding until just combined after each addition. Pour into cooled crust. Refrigerate until set, at least 2 hours or overnight.