01 - Preheat the oven to 350°F. Line an 8-inch square baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a bowl, combine graham cracker crumbs, sugar, melted butter, and salt. Mix until the crumbs are evenly moistened.
03 - Press the mixture firmly into the bottom of the prepared pan to form an even crust. Bake for 8-10 minutes until lightly golden. Let cool slightly.
04 - In a separate bowl, whisk together sweetened condensed milk, egg yolks, lime juice, lime zest, and green food coloring (if using) until smooth and fully combined.
05 - Pour the lime filling over the cooled crust, spreading evenly.
06 - Bake for 15-18 minutes, until the center is set but still slightly jiggly.
07 - Remove from oven and let cool to room temperature. Chill in the refrigerator for at least 1 hour before cutting.
08 - Use the parchment to lift the bars from the pan. Dust with powdered sugar and garnish with lime slices or zest if desired. Cut into 16 squares and serve chilled.