Line an 8x8 glass baking dish with a piece of parchment paper and preheat the oven to 350 degrees. In a large bowl, whisk the melted butter together with the sugars. Add the eggs and vanilla, and mix until fully combined.
Mix in the dry ingredients just until incorporated. Scrape down the sides of the bowl as needed.
Break the Lotus Biscoff cookies into chunks. Fold the cookies and the white chocolate into the wet ingredients using a rubber spatula.
Pour half of the blondie batter into the prepared baking pan.
Microwave the spread for 15 seconds, or until it's pourable. Pour the Biscoff cookie butter spread over the bottom layer of the blondies. Top with the remaining batter.
Gently press the remaining cookies on top, along with the chocolate, if desired. Bake for 35-40 minutes or until the buttery bars are golden brown across the top. Allow the blondies to cool.
Lift the blondies out of the pan by the edges of the parchment paper. Slice into bars and serve.