Directions

1. Preheat oven to 350 degrees. Process graham crackers and 2 tablespoons sugar in a food processor until fine crumbs form, add butter. Process until combined. Transfer mixture to a 9-inch tart pan with a removable bottom, pat into bottom and up sides. Place pan on a baking sheet, and bake until crust is fragrant and slightly colored, about 10 minutes.
2. Meanwhile, in a medium bowl, combine condensed milk, lime juice, egg yolks, remaining 1/2 cup sugar, and salt; whisk until smooth. Pour mixture into crust (warm or cool is fine), leaving 1/8 inch at the top; return to oven. Bake until filling is set around edge but still slightly loose in center, 20 to 25 minutes.
3. Cool completely at room temperature, then refrigerate until chilled, at least 2 hours. To store longer, cover and refrigerate, up to 2 days. Serve, garnished with zest, if desired.