Preheat oven to 350°F (175°C). Wrap the springform pan in two layers of heavy-duty foil.
Combine graham cracker crumbs, sugar, and salt. Stir in melted butter. Press into bottom and up the sides of the pan. Bake for 10 minutes, then reduce oven to 325°F (165°C).
In a food processor, pulse 1 cup of sugar with the lemon zest until fragrant and yellow-green. Whisk in remaining sugar and flour.
Beat cream cheese until smooth. Add lemon-sugar mixture, sour cream, vanilla, and lemon juice. Add eggs one at a time on low speed, mixing just until combined.
Pour filling into prepared crust. Place pan in a roasting pan and add 1 inch of hot water. Bake at 325°F for 55-70 minutes until edges are set and center jiggles.
Turn off oven and crack the door open. Leave cheesecake inside for 1 hour. Remove, run a knife around the edges, and cool completely on a wire rack.
Refrigerate for at least 4 hours or overnight until fully chilled.
In a saucepan, whisk eggs, sugar, lemon juice, zest, and salt. Cook over medium-low heat, whisking constantly, until thickened. Remove from heat and whisk in butter.
Strain curd if desired. Press plastic wrap onto the surface and refrigerate until cool.
Remove springform ring. Spread cooled lemon curd over the top of the cheesecake. Refrigerate for 30 minutes to set.
Beat heavy cream with powdered sugar and vanilla to stiff peaks. Pipe or spread around the border.
Slice with a warm knife for clean pieces. Serve chilled.