1. Crust: Preheat oven to 350 degrees Fahrenheit. Line 8-inch square baking pan with parchment paper and spray generously with cooking spray.
2. Combine graham crackers, butter, sugar and salt in a medium bowl. Combine until graham cracker crumbs are evenly moistened. Transfer to prepared baking pan and press firmly into bottom of pan. Bake until deeper in color and dry, 10 to 15 minutes. Transfer to wire rack and let cool completely.
3. Filling: In large bowl, combine cream cheese, zest, condensed milk, and yolk. Whisk vigorously until smooth. Add lime juice and stir until well combined.
4. Pour filling into crust and use spatula to spread into even layer that reaches to corners of pan. Bake until filling is just set, rotating pan halfway through, about 15 minutes. Remove from oven and cool to room temperature on wire rack, then cover with aluminum foil and refrigerate at least 4 hours.
5. Remove from pan, cut into squares and serve.
Reprinted with permission from JewishBoston.com.