Preheat oven to 350F. Line a 9x13-inch baking dish with aluminum foil, with ends of foil extending over the side. 

In a mixing bowl, combine graham cracker crumbs, sugar, and butter until all crumbs are moistened. Press into the bottom of the prepared pan. 

In a stand mixer fitted with the whisk attachment, beat cream cheese until smooth. Add lime zest, salt, sweetened condensed milk, key lime juice, and egg. Beat until well combined. 

Pour cheesecake over the crust, using a spatula to smooth the top. 

Bake 25 - 30 minutes, until the cheesecake is set. It will jiggle just a little bit. Let cool on a wire rack until room temp. Refrigerate several hours before trying to cut. 

Serve with whipped cream and lime slices.