Preheat your oven to 350°F (175°C). Line an 8x8 inch baking pan with parchment paper and set it aside.
In a medium bowl, combine the flour, baking powder, and salt. Set aside.
In a separate large mixing bowl, whisk together the melted butter and Biscoff cookie butter until smooth and well combined.
Add the brown sugar and granulated sugar, and whisk until smooth and creamy.
Add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract until fully incorporated.
Gradually add the dry ingredients to the wet ingredients, mixing gently with a spatula until just combined.
Fold in the roughly chopped white chocolate until evenly distributed.
Transfer the batter into the prepared baking pan and spread it out evenly.
Drizzle the melted Biscoff cookie butter over the top (if using), and sprinkle with roughly broken Biscoff cookies. Press them down gently.
Bake for 25-30 minutes or until the edges are golden brown and a toothpick inserted into the center comes out mostly clean (a few moist crumbs are fine).
Allow the blondies to cool completely in the pan before slicing.
Cut into squares and enjoy these delicious Biscoff blondies warm or at room temperature.