Measure out the vanilla ice cream, milk, sugar, and ice cubes, then set everything nearby for easy access.
Add the vanilla ice cream, milk, and sugar into the blender. Secure the lid tightly.
Pulse the blender a few times to break up the larger ice cubes, then blend on high for about 30-40 seconds until the mixture is thick, frosty, and smooth, with visible icy particles throughout.
Stop the blender and check the texture; it should be creamy yet with a noticeable icy crunch. If too thick, add a splash more milk and blend briefly.
Pour the milkshake slushie into tall glasses, filling them almost to the top to showcase the icy texture.
Serve immediately with a straw or spoon to enjoy the thick, icy-smooth texture and bursting flavors.