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 ½ cup of unsalted butter and ¾ cup of Biscoff cookie butter over low heat in a saucepan until combined and smooth.

Whisk in 1 cup of brown sugar until smooth, then add 2 eggs one at a time, mixing well after each, followed by 1 teaspoon of vanilla extract.

In a separate bowl, sift together 1.5 cups of all-purpose flour, 1 teaspoon of baking powder, and 0.25 teaspoon of salt, then gently fold into the wet batter.

Fold in 1 cup of white chocolate chips and 0.5 cup of crushed Biscoff cookies until evenly distributed.

Pour the batter into the prepared pan, spread evenly, and bake for 25-30 minutes.

Allow the blondies to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before cutting.