Preheat the oven to 180°C (350°F) and line a baking tray with baking paper.
With an electric mixer, beat the softened butter until creamy and add the brown sugar and sugar creaming them together.
Add the eggs one at a time beating well in between. Add the vanilla extract.
In a separate bowl, mix the flour and baking soda together.
Add the flour mixture to the wet ingredients in batches. The batter will be quite stiff.
Add the chocolate chips and stir in.
Divide the Oreos in half and place a marshmallow and piece of chocolate on one half and top that with the remaining half of the Oreo. You should have 15 S'moreo stacks.
Flatten a piece of cookie dough in your hand and place a S'moreo stack in the middle of the flattened dough. Wrap around the stack and seal the edges together around the Oreo and place on the baking tray.
Bake for around 10-12 minutes. The dough will still be a little soft to the touch.