Preheat your oven to 350°F (175°C) and prepare a 9x9-inch baking pan by greasing it or lining it with parchment paper.

Melt together the unsalted butter and Biscoff cookie butter in a saucepan over low heat for about 5 minutes, stirring frequently.

Add the brown sugar to the melted butter mixture, mixing well and allowing it to cool slightly.

Whisk in the eggs and vanilla extract until fully combined, creating a rich batter.

In a different bowl, sift together the flour, baking powder, and salt; then add to the wet mixture slowly, stirring gently.

Fold in the white chocolate chips and crushed Biscoff cookies until evenly dispersed.

Pour the batter into the prepared pan, spreading it evenly with a spatula.

Bake for 25-30 minutes, checking doneness with a toothpick.

Cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Cut into squares and serve the Biscoff Blondies.