Add the Oreo cookies to a blender and pulse a few times to break them into smaller chunks.
Add ice cubes to the mixture to help achieve a cold, slushy texture.
Secure the lid and blend on high until the mixture is smooth, thick, and icy—about 30-45 seconds. You should see the mixture turn a uniform chocolate color and become frosty on the sides of the blender jar.
Stop the blender and check the consistency; if it's too thick, add a splash more milk and blend briefly to loosen it up. If it’s too thin, add a few more ice cubes and blend again.
Once the slushie is creamy, cold, and well-blended, pour it into chilled glasses or bowls.
Serve immediately, optionally garnished with crushed Oreos or a whipped topping for extra indulgence.