In small saucepan, sprinkle unflavored gelatine over 1/4 cup milk; let stand 1 minute.
Stir over low heat until gelatine is completely dissolved, about 5 minutes.
In blender, process remaining 1/4 cup milk, syrup, sweetener and vanilla until blended.
While processing, through feed cap, gradually add gelatine mixture and process until blended.
Add ice cubes, 1 at a time; process at high speed until ice is melted.