Directions

1. Combine sugar, 1 teaspoon lime zest, and ½ teaspoon salt in a small bowl and rub zest into sugar and salt with your fingers until mixture looks like wet sand.
   
2. Transfer to a food processor, add graham crackers, and pulse to very fine crumbs. Add 1 egg yolk and butter and pulse until combined. Mixture should hold together when squeezed in the palm of your hand.
   
3. Place a rack in middle of oven; preheat to 375°. Transfer mixture to a 9” pie pan. Using your hands and the bottom of a flat measuring cup, press mixture evenly and firmly into bottom and up sides of pan.
   
4. Place pan on a rimmed baking sheet and bake crust until edges are golden brown, 12–14 minutes. (If crust slumps while baking, carefully press up sides again with measuring cup.) Transfer pan to a wire rack and let crust cool. Reduce oven temperature to 325°.
   
5. Gently whisk 6 large egg yolks, condensed milk, 2 teaspoons grated lime zest, lime juice, ¼ teaspoon salt, and vanilla extract in a large bowl just to combine (be careful not to beat in too much air).
   
6. Pour filling into cooled crust and bake pie until edges of filling are set but center still jiggles slightly when gently shaken, 20–22 minutes. Transfer pie to rack and let cool 1 hour, then chill, covered, at least 6 hours.
   
7. Just before serving, using an electric mixer on medium-high speed, beat heavy cream and a large pinch of salt in a medium bowl until medium peaks form. Add powdered sugar and beat, starting on low speed and moving up to medium-high as sugar is incorporated, until stiff peaks form.
   
8. Scrape whipped cream into center of pie and spread out to edges with an offset spatula, swooshing decoratively. Scatter lime zest over.