Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius). Line a 9x9-inch square baking pan with aluminum foil or parchment paper, and set aside.
In a large Ziploc bag, crush the graham crackers with a rolling pin until fine crumbs form. If using a food processor, pulse until fine crumbs are achieved.
In a medium mixing bowl, combine the crumbs, sugar, salt, and melted butter. Mix until well combined. Press the crumbs evenly into the bottom of the lined pan. Place in the oven and bake for 10 minutes.
Meanwhile, in a large mixing bowl with a hand mixer or a stand mixer fitted with the whisk attachment, beat the cream cheese until smooth and creamy. Add the condensed milk and mix until fully combined.
Add the egg yolks one at a time, mixing well after each addition. Follow with the lime zest, juice, and vanilla extract, mixing until fully combined.
Pour the key lime filling over the hot, baked crust. Return to the oven and bake for 15-18 minutes or until set. The top should not brown. Remove from the oven and chill in the refrigerator for 2-4 hours before serving.
Cut into squares and serve.
Notes
-Total time does not include chilling time.STORE the Key Lime Pie Bars in an airtight container in the refrigerator for up to 5 days. To FREEZE, wrap bars individually and place them in a freezer-safe bag, storing them for up to 3 months.Thaw in the refrigerator before serving. It's best served chilled for the best texture and flavor.