Prep the pan: Line an 8x8-inch square pan with parchment, leaving overhang on two sides for easy lifting. Lightly grease the other sides.
Make the crust: Stir crumbs, melted butter, sugar, and a pinch of salt until evenly moistened.
Press firmly into the pan, packing it tightly with the bottom of a measuring cup. Chill while you make the filling.
Melt the white chocolate: Place chopped white chocolate in a heatproof bowl. Microwave in 15–20 second bursts, stirring often, until smooth.
Or melt over a double boiler. Let cool to lukewarm—still fluid but not hot.
Beat the cream cheese: In a large bowl, beat cream cheese until very smooth and fluffy, about 2 minutes. Add powdered sugar, vanilla, lemon juice, and salt.
Mix until no lumps remain.
Add sour cream: Beat in sour cream or Greek yogurt until silky. Scrape the bowl so everything is combined.
Incorporate the white chocolate: With the mixer on low, stream in the cooled melted white chocolate. Mix just until uniform.
The mixture will thicken slightly.
Whip the cream: In a separate bowl, whip cold heavy cream to medium-stiff peaks. It should hold shape but still look glossy.
Fold it in: Gently fold the whipped cream into the cheesecake batter in two additions, keeping as much air as possible.
Fill and smooth: Pour over the chilled crust. Smooth the top with an offset spatula.
Tap the pan gently to release air bubbles.
Chill to set: Cover and refrigerate at least 6 hours, preferably overnight, until firm enough to slice cleanly.
Finish and serve: Lift out using the parchment. Slice into bars with a hot, dry knife, wiping between cuts. Top with berries, curls, or a tart sauce if you like.