Prepare the Pan: Start by lining an 8x8 inch baking dish with parchment paper, allowing for overhang on the sides for easy removal later.
Mix the Base: In a mixing bowl, combine the Biscoff cookie crumbs and melted butter. Stir until the mixture resembles wet sand.
Flatten the Mixture: Press the cookie crumb mixture firmly into the bottom of the prepared baking dish, creating an even base.
Melt the Chocolate: In a microwave-safe bowl, melt the dark chocolate chips in 30-second increments, stirring in between, until smooth and fully melted.
Mix in Marshmallows: Once melted, fold in the mini marshmallows. The warmth from the chocolate will gently soften the marshmallows.
Pour the Mixture: Pour the chocolate and marshmallow mixture over the crust, spreading it evenly to cover the base.
Add Toppings: If desired, crumble extra Biscoff cookies on top for a gorgeous finish and added crunch. You can sprinkle some sea salt for a sweet and salty vibe.
Chill: Place the dish in the refrigerator for about 1-2 hours or until set. Once chilled, lift out using the parchment overhang and cut into squares.