Preheat your oven to 350°F (175°C) and line an 8x8-inch baking pan with parchment paper.

In a medium bowl, combine crushed Biscoff cookies with melted salted butter, and press the mixture into the bottom of the pan.

In a large mixing bowl, whip together eggs, granulated sugar, and light brown sugar until light and creamy, about 2-3 minutes. Include melted butter and vanilla extract until fully combined.

Sift in flour, cocoa powder, and baking powder into the egg mixture. Fold until just combined to keep the blend rich and fudgy.

Pour the brownie batter over the cookie crust, spreading evenly across the surface.

Heat Biscoff spread slightly in the microwave; dollop spoonfuls on the brownie batter and swirl with a knife.

Bake for 22-25 minutes, checking doneness with a toothpick. Remove once slightly moist crumbs stick.

Cool in the pan for 15 minutes, then transfer to a wire rack to cool completely before slicing.