Preheat oven to 325° F. Grease an 8-inch square baking pan, line with parchment paper and set aside.
In the bowl of a food processor, crush graham crackers into fine crumbs, about 30 seconds (you can also place graham crackers in a zip-top bag and crush them with the back of a measuring cup). Add sugar and melted butter. Process until combined, about ten 1-second pulses.
Transfer mixture to prepared pan. Press the graham cracker crumbs into the bottom of the pan. Bake for 15 minutes or until fragrant. Cool completely. While the crust is baking, prepare the filling.
Key Lime Pie Filling
In a large bowl, whisk egg yolks and lime zest together until the mixture turns greenish yellow, about 2 minutes. Add sweetened condensed milk and whisk until combined. Add fresh lime juice and whisk until incorporated. Let the mixture sit at room temperature to thicken, about 30 minutes.
Pour the lime filling into the graham cracker crust. Bake for 15 to 17 minutes or until the center is set, but still jiggles slightly.
Let bars cool on a wire rack until it reaches room temperature, then transfer it to the refrigerator to chill for 3 hours.
Cut into 16 bars, garnish with a dollop of whipped cream and lime slices or zest.
Notes
Store key lime pie bars in an airtight container in the refrigerator for up to 3 days.Lime juice: Regular limes may be used in this recipe. I do not recommend store-bought lime juice as it does not have enough flavor. If you must use store-bought, only use Nellie & Joe Key Lime Juice.Recommended tools: Mini food processor, 8x8 pan, mixing bowls, citrus juicer and zester.