Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking pan.

In a large mixing bowl, whisk together melted butter and brown sugar until glossy.

Add eggs one at a time and vanilla, mixing well until smooth.

In a separate bowl, sift together flour, baking powder, salt, and cinnamon; then fold into wet mixture.

Drop dollops of Biscoff spread into the batter and gently swirl.

Transfer the batter to the prepared pan and bake for 20-25 minutes.

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