Prep the pan: Line the bottom of a 9-inch springform pan with parchment.
Lightly grease the sides if you like for clean edges.
Make the crust: Stir graham crumbs, sugar, and salt with the melted butter until evenly moistened. Press firmly into the bottom of the pan, using the bottom of a measuring cup to compact. Chill while you make the filling and swirl.
Cook the raspberry sauce: In a small saucepan, combine raspberries, sugar, and lemon juice over medium heat.
Cook 3–5 minutes, stirring and mashing until juicy and bubbling.
Thicken and strain: Stir in the cornstarch slurry and cook 1 more minute until slightly thickened. Push through a fine-mesh strainer to remove seeds. Let it cool to room temperature.
It should be pourable but not watery.
Bloom the gelatin (optional): Sprinkle gelatin over 3 tablespoons cold water in a small bowl. Let stand 5 minutes, then warm gently in the microwave in 5–10 second bursts until dissolved and clear. Cool to lukewarm.
Beat the cream cheese: In a large bowl, beat cream cheese, sugar, salt, vanilla, and lemon juice until smooth and fluffy, about 2 minutes.
Scrape the bowl.
Add sour cream: Mix in sour cream until silky.
Whip the cream: In a separate bowl, whip heavy cream to medium-stiff peaks. Don’t overbeat.
Stabilize (if using gelatin): With the mixer running on low, stream the lukewarm dissolved gelatin into the cream cheese mixture. Mix just to combine.
Fold it together: Gently fold the whipped cream into the cream cheese base in two additions until no streaks remain.
The mixture should be thick and airy.
Assemble: Spoon half the cheesecake filling over the chilled crust and smooth the top. Drizzle a few spoonfuls of raspberry sauce and swirl gently with a skewer or butter knife. Add the remaining filling, smooth again, then dot more raspberry sauce and swirl lightly on the surface.
Reserve any extra sauce for serving.
Chill to set: Cover the pan and refrigerate at least 6 hours, ideally overnight, until firm enough to slice cleanly.
Release and serve: Run a thin knife around the edge, unclasp the ring, and transfer to a platter. Slice with a hot, dry knife for neat wedges. Serve with extra raspberry sauce if desired.