Preheat oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper.
Melt butter and mix with sugar until smooth.
Add eggs and vanilla extract, mixing until well combined.
Sift in flour, cocoa powder, and salt. Fold until just combined.
Stir in chocolate chips.
Pour half of the brownie batter into the prepared pan.
Warm the Biscoff spread slightly and drop spoonfuls onto the batter.
Use a knife or skewer to swirl the Biscoff spread into the batter.
Add the remaining brownie batter and more spoonfuls of Biscoff spread on top. Swirl again.
Sprinkle crushed Biscoff cookies over the top.
Bake for 25-30 minutes, until the edges are set but the center is slightly soft.
Let the brownies cool before cutting into squares. Enjoy!