MAKE CRUST; Adjust oven rack to middle position and heat oven to 350 degrees. Process cookies in food processor until finely ground. Add butter and zest and pulse until combined. Press mixture into bottom of 9-inch springform pan. Bake until lightly browned and set, about 10 minutes. Cool completely on wire rack, at least 30 minutes.
MAKE CURD; While crust is cooling, whisk egg, egg yolk, sugar, and salt together in small saucepan. Add lemon juice and cook over medium-low heat, stirring constantly, until thick and puddinglike, about 3 minutes. Remove from heat and stir in butter and cream. Press through fine-mesh strainer into small bowl and refrigerate until needed.
SOFTEN GELATIN: Combine lemon juice and gelatin in small bowl and let stand until gelatin softens, about 5 minutes. Microwave until mixture is bubbling around edges and gelatin dissolves, about 30 seconds. Set aside.
MAKE FILLING: With electric mixer on medium speed, beat cream cheese, sugar, and salt until smooth and creamy, scraping down sides of bowl, about 2 minutes. Slowly add cream and beat until light and fluffy, about 2 minutes. Add gelatin mixture and ¼ cup curd, increase speed to medium-high, and beat until smooth and airy, about 3 minutes.
CHILL CHEESECAKE: Pour filling into cooled crust and smooth top. Pour thin lines of remaining curd on top of cake and lightly drag paring knife or skewer through lines to create marbled appearance. Refrigerate until set, at least 6 hours. Remove sides of pan. Serve. (Cheesecake can be covered in plastic wrap and refrigerated for up to 3 days.).