Preheat your oven to 350°F (175°C) and prepare an 8×8-inch baking pan by greasing it well.

Melt the butter in a medium saucepan over low heat. Stir in the granulated and brown sugars until smooth and glossy, about 2-3 minutes.

Cool the mixture slightly before whisking in the eggs one at a time, and add the vanilla extract.

In a separate bowl, combine the flour, cocoa powder, and a pinch of salt. Fold this mixture into the wet ingredients until just combined.

Swirl half of the Biscoff spread into the batter and fold in the crushed Biscoff cookies.

Spread the brownie batter into the prepared pan. Dollop the remaining Biscoff spread on top and swirl it gently. Bake for 25-30 minutes until a toothpick comes out with a few moist crumbs.