Preheat the oven to 300 degrees. Position the oven racks so one is just above the middle position and the other is just below the middle position. Lightly spray a 9-inch springform pan with cooking spray.
In a medium bowl, stir together the graham cracker crumbs, sugar, and melted butter. Mix until the graham cracker crumbs are evenly coated. Press the mixture into the bottom and up the sides (about 1/2" up) of the prepared springform pan.
Bake the crust for 15 minutes. Remove from the oven and let cool completely while you prepare the filling.
In a large bowl with an electric mixer, or in the bowl of an electric stand mixer, beat the cream cheese, sugar, cornstarch and lime zest together until smooth and creamy. Scraping down the sides of the bowl as needed. Add the key lime juice and mix until combined. Add the eggs and mix until just combined. Over mixing can cause the cheesecake to crack while baking because of all the extra air beat into the filling, so be sure to mix just until combined and creamy.
Pour the cheesecake filling over the crust and spread evenly.
Place a metal or glass 9X13-inch pan (or similar-sized pan) on the bottom rack of the oven and pour in 3 cups of boiling water. Immediately place the cheesecake on the upper rack and bake for 55-65 minutes until the cheesecake is set around the edges. A slight jiggle in the center of the cheesecake is fine.
When cook time is done, turn the oven off and prop the oven door open about 4 inches. Keep the cheesecake in the oven for 30 minutes. Remove and let cool completely on a cooling rack.
Refrigerate the cheesecake overnight.
When ready to serve, whip together the cream and powdered sugar until thick and creamy. Either spread the whipped cream evenly over the cheesecake or pipe it around the edges, or just dollop a spoonful on each individual piece. If wanted, garnish with lime slices or lime zest.