- Pre-heat oven to 180C (350F). Grease a 9-inch springform pan.
- In a medium bowl mix together cookie crumbs, sugar, and butter until combined and wet sand-like texture. Press into the base of the springform pan and use the back of a spoon or small bowl to press in.
- Bake for 10 minutes, set aside to cool.
- In a large microwavable bowl melt chocolate and butter together. Stir in both sugar and then eggs into a smooth batter. Fold in flour and chopped chocolate pieces until just combined.
- Pour caramel sauce over cooled cookie base. Pour brownie mix over top and spread to the edges, evenly. Bake in the oven for 35-40 minutes until a toothpick comes out with some crumbs, just set.
- Sprinkle marshmallows over entire top of brownie and place under the grill for 2-3 minutes to toast marshmallows. Keep a close eye on them to not burn.
- Let cool for 30 minutes and cut.