Preheat oven to 180°C (350°F).
Crush Biscoff cookies in a food processor until fine.
Mix with melted butter and sugar (if using).
Press into the bottom of a 9-inch springform pan.
Bake for 10 minutes, then cool.
Beat cream cheese until smooth.
Add sugar, sour cream, and vanilla; mix well.
Add eggs one at a time, mixing after each.
Fold in the Biscoff spread until combined.
Pour filling over the cooled crust.
Bake for 50-60 minutes until edges are set.
Turn off the oven and crack the door; cool for 1 hour.
Refrigerate for at least 4 hours, preferably overnight.
Top with whipped cream and crushed Biscoff cookies before serving.