Prep the pan: Line a 9-inch (23 cm) springform pan with parchment on the base. Lightly grease the sides.
Make the crust: Stir Biscoff crumbs with melted butter, sugar, and salt until it looks like wet sand. Press firmly into the pan, going slightly up the sides.
Chill 15–20 minutes.
Bloom the gelatin (if using): Sprinkle gelatin over cold water and let sit 5 minutes. Microwave 10–15 seconds to dissolve, then cool slightly. If using whipped cream instead, skip this step and whip the cream to soft peaks.
Beat the base: In a large bowl, beat cream cheese until smooth.
Add Greek yogurt, Biscoff spread, powdered sugar, vanilla, lemon juice, and salt. Mix until silky with no lumps.
Set the filling: Gelatin method: With mixer on low, stream in the dissolved gelatin. Mix just to combine.
Whipped cream method: Gently fold whipped cream into the filling with a spatula until uniform.
Fill and chill: Pour filling over the crust and smooth the top.
Tap the pan to release air bubbles. Chill at least 6 hours, preferably overnight, until firm.
Finish: Warm Biscoff spread until pourable and drizzle over the top. Add crushed cookies for texture.
Slice with a hot knife for clean edges.