Preheat your oven to 350°F (175°C). Grease a 9x9-inch baking pan or line with parchment paper.

In a medium saucepan over low heat, combine the unsalted butter and Biscoff cookie butter. Stir until smooth and melted (3-5 minutes).

Remove from heat, and let cool for about 5 minutes. Whisk in the brown sugar until smooth and glossy.

Add the eggs one at a time, whisking thoroughly after each addition until the batter is smooth and thick.

Mix in the vanilla extract, stirring gently until evenly distributed.

In a separate bowl, sift together the flour, baking powder, and salt.

Gradually fold the dry ingredients into the wet mixture until just combined, avoiding overmixing.

Gently fold in the white chocolate chips and crushed Biscoff cookies.

Pour the batter into the prepared baking pan, spreading evenly.

Bake for 25-30 minutes. Start checking at 25 minutes; toothpick should come out clean or with a few moist crumbs.

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

Slice into squares and serve as a delightful treat.