Add the chilled milk, crushed Oreos, and ice cubes to your high-speed blender.
Secure the lid on the blender and blend on high for about 30-45 seconds until the mixture is smooth, thick, and icy with a gritty texture from the Oreos.
Stop the blender and check the consistency—if it’s too thick, add a splash of milk, then blend briefly to loosen it up; if too thin, add a few more crushed Oreos and pulse a few seconds.
Pour the slushie into chilled glasses, observing the swirling dark and creamy layers that form from the Oreos.
Serve immediately with a straw or spoon, enjoying the cold, gritty texture and rich Oreo flavor.