Prepare the crust: Combine graham cracker crumbs, sugar, and melted butter in a medium bowl. Mix until well combined. Press into the pan: Press the crumb mixture firmly into the bottom of a 9-inch springform pan. You can use the bottom of a measuring cup or glass to create an even crust.
Pre-bake (optional): Baking the crust for 8-10 minutes at 350°F (175°C) before adding the filling can help prevent a soggy crust. Let cool completely before adding the filling.
Beat cream cheese and sugar: In a large bowl, beat cream cheese and sugar together until smooth and creamy. Add eggs: Beat in eggs one at a time, mixing well after each addition. Be careful not to overmix.
Incorporate remaining ingredients: Gently fold in sour cream, mango puree, key lime juice, vanilla extract, cornstarch (if using), and salt. Mix until just combined.
Water bath (recommended): Wrap the bottom of the springform pan tightly with aluminum foil to prevent water from leaking in. Place the springform pan in a larger roasting pan or baking sheet. Pour hot water into the roasting pan until it comes halfway up the sides of the springform pan. This creates a humid environment and helps prevent cracking. Bake: Bake in a preheated oven at 350°F (175°C) for 50 minutes, or until the cheesecake is set around the edges but still slightly jiggly in the center.
Cool down: Turn off the oven and leave the cheesecake in the oven with the door slightly ajar for 1 hour. This allows the cheesecake to cool gradually and minimizes cracking.
Refrigerate: Remove the cheesecake from the oven and carefully remove it from the water bath. Let it cool completely on a wire rack before covering and refrigerating for at least 4-6 hours, or preferably overnight.
Release from pan: Carefully run a thin knife around the edges of the cheesecake to loosen it from the pan. Release the springform pan.
Slice and serve: Slice the cheesecake and serve chilled. Garnish with fresh mango slices, whipped cream, or a drizzle of key lime curd, if desired.