01 - Preheat oven to 350°F. Line an 8×8-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a medium bowl, combine graham cracker crumbs, sugar, melted butter, and salt. Mix until evenly moistened. Press the mixture firmly into the bottom of the prepared pan to form an even crust.
03 - Bake the crust for 8–10 minutes, until lightly golden. Remove from oven and let cool slightly.
04 - In a separate bowl, whisk together sweetened condensed milk, egg yolks, lime juice, and lime zest until smooth and well combined.
05 - Pour the lime filling over the cooled crust and spread evenly.
06 - Bake for 15 minutes, until the filling is just set and barely jiggles in the center.
07 - Remove from oven and cool to room temperature. Then refrigerate for at least 1 hour, until fully chilled.
08 - For the optional topping, whip heavy cream with powdered sugar until soft peaks form. Spread or pipe over chilled bars and garnish with lime zest.
09 - Lift bars out of the pan using parchment overhang. Cut into squares and serve chilled.