Preheat the oven to 350°F. Line an 8x8 glass baking dish with parchment paper and set it aside.

In a large mixing bowl, whisk together the melted butter, granulated sugar, and brown sugar.

Add the vanilla extract and eggs and continue whisking until fully combined.

Add the salt, flour, and baking powder to the butter/egg mixture and stir just until incorporated.

Chop or break the Biscoff cookies into chunks. Add the cookie pieces and white chocolate into the blondie batter and stir briefly to distribute. (Reserve a few pieces of chocolate and cookie chunks for the top of the blondies, if desired.)

Spread HALF of the batter into the prepared baking dish.

Microwave the Biscoff for 15 seconds until it is pourable. Pour over the bottom layer of blondies. Top with the remaining blondie batter.

Press additional cookie pieces and/or white chocolate across the top.

Bake blondies for 35 to 40 minutes or until they are golden brown across the top and a knife inserted in the center comes out clean or with a few crumbs clinging. The center should not be wet.

When the blondies are cooled completely, lift them from the baking dish by pulling the overhang of the parchment paper liner. Cut into bars and serve.