Lemon Chiffon Pie with Saltine Cracker Crust

Preheat oven to 350°F. Stir together crackers and sugar in a medium bowl. Add butter; knead with your hands until mixture holds together. Press into bottom and up sides of a 9-inch deep-dish pie pan. Chill 15 minutes. Bake in preheated oven until lightly browned, about 15 minutes. Let cool completely on a wire rack, about 1 hour.

Stir together 1/4 cup cold water and gelatin in a small bowl; let stand until softened, about 5 minutes. Meanwhile, beat egg yolks with an electric mixer on high speed until thick and lemon-colored, about 1 minute and 30 seconds. Transfer to a medium saucepan. Add 1 cup sugar, lemon zest and juice, and salt; stir until smooth. Cook mixture over low, stirring constantly using a rubber spatula and scraping down sides of pan constantly, until mixture is thickened, 5 to 8 minutes. (Do not let eggs scramble. If mixture becomes too hot, temporarily remove pan from heat, stirring constantly, until slightly cooled.) Remove from heat; add gelatin mixture, and stir until dissolved. Let cool, stirring occasionally, 1 hour. Transfer to a large bowl; set aside.

Beat heavy cream with an electric mixer on high speed until stiff peaks form, about 45 seconds. Set aside.

Beat egg whites in a medium bowl with an electric mixer on medium speed until foamy, about 20 seconds. Gradually beat in remaining 1/2 cup sugar. Increase mixer speed to high; beat until stiff peaks form, about 3 minutes.

Whisk about 1 cup egg white mixture into cooled lemon mixture. Add half of the remaining egg white mixture and half of the whipped cream to lemon mixture; using a spatula, fold in until almost combined. Add remaining egg white mixture and whipped cream; fold in until just combined. Spoon into crust. Chill until set, about 1 hour.

If desired, beat cream with an electric mixer on high speed until stiff peaks form, about 45 seconds; dollop over chilled pie. Garnish with lemon slices.