Step 1: Prepare the Crust. In a mixing bowl, combine crushed graham crackers, melted unsalted butter, and granulated sugar. Stir until the mixture resembles wet sand. Press this mixture firmly into the bottom of a greased 9-inch springform pan, spreading it evenly. Bake in a preheated oven at 325°F for 10 minutes until golden and fragrant, then let it cool while you prepare the filling.

Step 2: Waterproof the Pan. Wrap the exterior of the springform pan with a layer of aluminum foil to prevent leaks.

Step 3: Mix Filling. Beat the cream cheese until fluffy. Gradually add granulated sugar and cornstarch. Blend in sour cream, key lime juice, zest, and vanilla until smooth. Add eggs one at a time, mixing just until combined after each addition.

Step 4: Bake Cheesecake. Pour the filling into the crust. Place the springform pan inside a roasting pan and add boiling water until it reaches halfway up the sides of the springform pan. Bake at 325°F for 65-85 minutes, until edges are set and center has a slight wobble.

Step 5: Cool. Turn off the oven and crack open the door slightly. Allow the cheesecake to cool for about an hour, then remove from water bath and let cool completely on a wire rack for 2-3 hours.

Step 6: Chill. Refrigerate the cooled cheesecake overnight for best flavor.

Step 7: Make Stabilized Whipped Cream. Dissolve unflavored gelatin in cold water. Whip heavy cream, powdered sugar, and vanilla until soft peaks form. Gradually add gelatin mixture, continuing to whip until stiff peaks form.

Step 8: Serve. Pipe the stabilized whipped cream onto the cheesecake. Garnish with fresh berries and lime zest if desired.