Preheat your oven to 350°F (175°C).

Combine melted butter, brown sugar, and granulated sugar in a mixing bowl. Use a whisk or spatula to blend them together until creamy and well incorporated.

Add the eggs and vanilla extract to your mixture; mix well until you achieve a smooth consistency.

Whisk together the flour, baking powder, and salt in another bowl.

Gradually mix the dry ingredients into the wet mixture, stirring until just combined.

Fold in the Biscoff cookie crumbs gently.

Spread the batter into a greased baking pan evenly.

Dollop Biscoff spread on top and use a knife to swirl it gently into the batter.

Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.

Cool for a few minutes in the pan before transferring to a wire rack.