Place milk in a medium-sized saucepan and add gelatin, cocoa, sugar and salt. Stir over moderate heat until gelatin is completely dissolved. Remove from heat; add vanilla and stir briskly with fork or wire whisk to mix ingredients well. Pour into blender, add ice cubes, cover and blend at medium speed until ice cubes dissolve. Uncover, stir once with rubber spatula and let stand 2-3 minutes to jell. Spoon into 4 dessert dishes or parfait glasses and top each serving with 1 tsp chocolate shavings.