Line a 13x9-inch pan with foil. The foil should extend over the sides of the pan.
Take a large microwaveable bowl. Add butter. Heat it on high power for 45 seconds or until melted.
Add the marshmallows. Toss it so that it's evenly coated. Heat it for 1½ minutes, stirring every 45 seconds, or until the marshmallows melt completely and the mixture is well-blended.
Add the rice cereal and chopped Oreo Cookies. Mix well.
Transfer the mixture to the prepared pan. Press it onto the bottom of the prepared pan. Let it cool completely.
Use the foil handles to remove the cereal mixture from the pan. Discard the foil.
Cut the cereal mixture crosswise into 8 strips. Take 5 strips and cut them crosswise into three parts. Take the remaining 3 strips and cut them crosswise into 5 rectangles.
Place 1 small rectangle on the center of each of the larger rectangles. Press it gently so it stays in the same position,
Decorate with the Mini Oreo Cookies and Gems as shown in the photo. Place 4 Oreo Cookies (2 on each side) vertically along the length of each of the bigger rectangles to form the wheels of the cars.
Use the gems to make the headlights. Secure the gems and the cookies with the melted Cadbury Dairy Milk Silk.
Refrigerate for 15 minutes or until firm. Oreo Crispy Treat Cars are ready!