Make the Crust: In a medium bowl, whisk together the cookie crumbs and sugar. Add the melted butter and, using a fork, stir together until evenly moistened. Press into the bottom and partway up the sides of a 9-inch springform pan. Set aside.
Make the Filling: Place the key lime juice in a medium saucepan over medium heat until warm to the touch. Whisk in 1/3 cup of the heavy cream and the gelatin until combined and bring to a simmer. Remove the pan from the heat, add the white chocolate, and stir until smooth. Allow the mixture to cool to room temperature.
In a small bowl, rub together the sugar the lime zest until all of the sugar has been moistened with the zest.
Using an electric mixer, beat the cream cheese and sugar mixture on medium speed until light, fluffy and smooth. Reduce the speed to medium-low and slow beat in the cooled white chocolate mixture until completely combined and smooth, scraping the sides of the bowl as needed.
In a clean bowl and with clean and dry beaters, beat the remaining 1 1/3 cups heavy cream until it forms soft peaks. Fold it into the cream cheese mixture, then pour it into the crust and smooth the top into an even layer.
Cover the cheesecake with plastic wrap and refrigerate overnight. Remove from the refrigerator, release the cheesecake from the springform pan and transfer to a serving plate. Leftover cheesecake can be stored, covered, in the refrigerator for up to 5 days.
Do not substitute bottled key lime juice; fresh key lime juice makes the flavor!
If you cannot find fresh key limes, use equal amounts of lime juice and lemon juice.
Do not use the zest of the key limes - the peel is too thin. Use regular limes for the zest in the recipe.
If you'd like a frozen texture, instead of refrigerating overnight, place the cheesecake in the freezer overnight and serve straight from the freezer. You can also wrap the cheesecake in plastic wrap, then foil, and freeze for up to 1 month.