STEP - 1
Preheat your oven to 375 degrees F (190 C). Prepare a 9x9 pan by lining it with aluminum foil and spraying the foil with nonstick cooking spray.
STEP - 2
Place the butter in a medium microwave-safe bowl and microwave it until it is melted. Once melted, stir in the sugar and graham cracker crumbs until everything is moistened and is the texture of wet sand.
STEP - 3
Scatter the crumbs in the bottom of the prepared pan, and press them into an even layer. Bake the bottom crust for 5 minutes, until it is fragrant and lightly colored along the sides. Remove from the oven and cool while you prepare the rest of the fudge.
STEP - 4
Place the chopped white chocolate, the sweetened condensed milk, and the salt in a large microwave-safe bowl, and microwave it in 30-second increments, stirring after every 30 seconds. Continue to microwave until the white chocolate is completely melted and your mixture is smooth.
STEP - 5
Add the lime juice and lime zest to the white chocolate and stir to incorporate it.
STEP - 6
Scrape the fudge into prepared pan and smooth it into an even layer on top of the graham cracker crust. Refrigerate the fudge until it is completely set, for about 2-3 hours or overnight.
STEP - 7
Once set, remove it from the pan using the foil as handles. Use a large sharp knife to cut it into 1-inch squares. It helps to rinse the knife in hot water periodically to get cleaner cuts.
STEP - 8
Store Key Lime Pie Fudge in an airtight container in the refrigerator for up to two weeks. For best taste and texture, let it sit at room temperature for 20 minutes before serving.