Pour heavy whipping cream, cocoa powder and powdered sugar into a bowl and whip using hand mixer/stand mixer or by hand until stiff peaks have formed.
Optional step Place about a cup of mini marshmallows on a sheet pan. Either put them under the broiler or use a chef's torch to lightly toast them. These marshmallows will go into the whipped cream. Toasting them first will give you a little of that toasty flavor but you can skip and just add straight from the bag into the whipped cream.
Line a loaf pan with parchment paper and place a very small amount on the bottom. You only need a tiny bit so the cookies don't slide around while you assemble the bottom layer.
Add about 1-2 cups of marshmallows to the chocolate whipped cream. How many you use is personal preference on whether you'd like more or less marshmallow flavor.
Place biscoff cookies in the bottom of the loaf pan filling the space. If necessary break cookies into smaller pieces to fill gaps.
Spread a layer of the whipped cream with marshmallows over the top of the cookies at least a half inch thick.
Repeat, layering more biscoff cookies over top of the whipped cream, and then adding another layer of whipped cream. End on a layer of whipped cream.
Chill cake in the refrigerator for at least 4-6 hours but overnight works best.
Optional When cake is ready, top with additional large marshmallows that have been toasted under the broiler or with a torch, and chocolate chips or chunks. Enjoy!