Preheat your oven to 350°F (175°C) and prepare an 8 x 8-inch baking pan by lining it with parchment paper.

In a mixing bowl, combine 1 1/2 cups of crushed Biscoff cookies with 1/4 cup of melted butter. Stir until the mixture resembles wet sand. Press this mixture into the bottom of the lined baking pan.

In a medium bowl, beat 2 large eggs, 1/2 cup granulated sugar, and 1/2 cup packed light brown sugar for about 1 minute until light and creamy.

Add 1/4 cup of melted butter and 2 teaspoons of vanilla extract to the egg and sugar mixture. Blend until fully incorporated.

Sift in 1/2 cup all-purpose flour, 1/3 cup unsweetened cocoa powder, and 1/4 teaspoon baking powder. Gently fold these dry ingredients into the wet mixture until just combined.

Carefully pour the brownie batter over the prepared crust in the baking pan, spreading it evenly.

Warm 1/3 cup of smooth Biscoff spread in the microwave for 5-10 seconds. Spoon dollops onto the brownie batter and gently swirl through with a butter knife.

Bake for 22-25 minutes, checking for doneness with a toothpick. Let cool completely in the pan.

Once cooled, lift the brownies out using the parchment paper and slice into squares.