Preheat the oven to 350°F and line an 8-inch square baking pan with parchment paper.
In a large mixing bowl, combine the melted butter, white sugar, and brown sugar; beat on high speed until smooth.
Add the eggs and vanilla extract and beat again on high speed until fully combined and voluminous.
Gradually add the flour and beat on low speed until the batter is fully combined.
Fold the white chocolate chips into the blondie batter using a spatula.
Transfer the batter to the prepared pan and spread it evenly with the back of a spoon or an offset spatula.
Warm the Biscoff spread in the microwave for about 30 seconds, then pour it over the blondie batter.
Use a knife to gently swirl the Biscoff spread into the blondie mixture.
Sprinkle the chopped Biscoff cookies on top and gently press them down with your hands.
Bake in the center of the preheated oven for 30 minutes.
Allow the blondies to cool completely in the pan before removing and slicing into 12 equal squares.
Serve drizzled with warm Biscoff spread and enjoy!
Notes
For thicker blondies, use an 8-inch pan. Storing overnight helps them set well and makes slicing easier. Biscoff cookies add a signature caramelized and spiced flavor.