Place the espresso in a flat, open bowl and have all your other ingredients ready.
Dip your first OREO cookie very briefly in the espresso and place it in your dish. Arrange the first layer of OREOS in an even 4 X 4 pattern in your dish. Sprinkle the OREO cookies with 1-2 teaspoons of cocoa or finely grated dark chocolate.
Top the OREO cookies with 1/3 of the cream mixture, dolloping it in different areas of the baking dish. Work carefully and gently to spread the cream out without disturbing the OREO cookies below. I like to use an offset spatula for this.
Repeat this layering twice more: 1-2 teaspoons of cocoa, espresso dipped OREO cookies, 1/3 of the cream. On the last layer, leave off the cocoa until you serve the Tiramisu. You will need to split 4-5 OREO cookies (carefully use a sharp knife to slice through the cream centre, splitting the OREO cookie in two) for the perfect amount of biscuits.
You should have a total of 3 layers of OREO cookies, 3 layers of cream and 3 layers of cocoa (with a fourth to come).
Cover the Tiramisu and place in the fridge for 3-4 hours (I like to leave it overnight).
When you are ready to serve, sprinkle the Tiramisu with 1-2 teaspoons of cocoa or finely grated dark chocolate. Slice the Tiramisu into 9-12 pieces and serve.
Leftovers keep well in the fridge for a number of days. They can also be frozen and defrosted.