In a medium bowl, combine graham cracker crumbs, sugar, and salt. Pour in the melted butter and mix until the texture resembles wet sand. Press the mixture firmly into the bottom and slightly up the sides of a 9-inch springform pan. Use the bottom of a measuring cup to create a smooth, even surface. Refrigerate while preparing the filling.
In a small microwave-safe bowl, sprinkle the gelatin over 3 tablespoons of cold water. Let it sit for 5 minutes to bloom. After blooming, microwave the mixture for 15-20 seconds until the gelatin dissolves completely. Set aside to cool slightly but don't let it solidify.
In a large bowl using an electric mixer, beat the cream cheese until smooth and creamy, about 2 minutes. Add the sugar and continue beating until well combined. Mix in the lemon juice, vanilla extract, and sour cream until smooth. With the mixer running on low speed, slowly pour in the dissolved gelatin mixture and mix until fully incorporated.
In a separate bowl, whip the heavy cream until stiff peaks form. Gently fold the whipped cream into the cream cheese mixture until fully combined, being careful not to deflate the mixture.
Pour the filling over the prepared crust, smoothing the top with a spatula. Tap the pan gently on the counter a few times to release any air bubbles. Cover with plastic wrap and refrigerate for at least 6 hours or overnight.
Combine the passion fruit pulp and sugar in a small saucepan over medium heat. In a separate small bowl, mix the cornstarch with 1 tablespoon of cold water to create a slurry. Once the passion fruit mixture begins to simmer, stir in the cornstarch slurry and cook for 1-2 minutes until thickened. Remove from heat and allow to cool completely.
Once the cheesecake has set and the topping has cooled, spread the passion fruit mixture over the cheesecake. Return to the refrigerator for an additional 30 minutes to set the topping. Before serving, carefully run a knife around the edges of the springform pan before releasing.