Measure out the chilled vanilla milk and pour it into your blender.
Add crushed ice to the blender, ensuring it's pre-chilled for the best icy texture.
If desired, pour in vanilla extract and sprinkle in sugar to boost the flavor and sweetness.
Secure the lid on the blender and blend on high speed for about 1 to 2 minutes, until the mixture is smooth and creamy with a velvety texture.
Stop the blender and check the consistency; it should be thick, icy, and well-incorporated, with a fragrant vanilla aroma.
Pour the vanilla creamy slushie into chilled glasses, and serve immediately with a straw or a garnish if desired.