Place the frozen Oreos in a blender bowl.
Add cold milk to the blender with the Oreos.
Secure the lid on the blender and blend on high speed until the mixture becomes thick, smooth, and evenly chocolate-colored, about 30-45 seconds. You should see the cookies breaking down and the mixture starting to swirl smoothly.
Pause briefly to scrape down the sides if necessary, then give it another quick blend to ensure everything is combined with some cookie chunks remaining for texture.
Pour the thick, icy Oreo mixture into glasses, letting it swirl and mound up with a slightly frosty surface.
Serve immediately with a straw or spoon, enjoying the creamy, chocolatey texture that’s perfect for a hot day.