Preheat your oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper.

In a microwave-safe bowl or saucepan, melt the butter and chopped chocolate until smooth. Let it cool slightly.

Whisk in the sugar until combined. Add eggs and vanilla, and whisk until the mixture is thick and glossy.

Sift in the flour, cocoa powder, and salt. Gently fold together until just combined—don’t overmix!

Pour half the batter into your prepared pan. Drop spoonfuls of half the melted Biscoff spread over the top and swirl with a toothpick or knife.

Add the remaining batter on top, followed by the rest of the Biscoff spread. Swirl again.

Sprinkle with crushed Biscoff cookies if using.

Bake for 25–30 minutes, or until the edges are set and a toothpick inserted comes out with a few moist crumbs.

Let the brownies cool completely in the pan before slicing. (They’ll firm up as they cool—promise it’s worth the wait!)