Preheat oven to 350 degrees F. Line a 13x9" baking pan with foil, extending the sides of the foil over the edges of the pan. Spray the foil liberally with cooking spray; set aside.

In a large bowl, combine the cake mix, melted butter and egg until a soft dough forms. Press evenly into the prepared pan. Sprinkle with the white chocolate chips.

Wipe out the bowl and add in the cream cheese. Beat until smooth, about 1 minute. Add in the Biscoff spread and beat to combine. Add in the eggs and melted butter, mixing carefully. Lastly, add in the powdered sugar until thick and combined.

Pour the filling mixture evenly over the base and bake for approx. 35-40 minutes or until the center is just about set and the bars are only slightly jiggly. They shouldn't be sloshing around in the pan, but a little jiggle is okay. Cool completely, then refrigerate for AT LEAST 2 hours, preferably overnight, before cutting into bars. Dust with powdered sugar before serving.