The fastest (and most practical) technique I found is wrapping a bottle [of milk] in a wet paper towel and putting it in the freezer. For an average half-liter-sized bottle, you will have deeply chilled milk in about 20-30 minutes.
Ice Cold Milk:Can be looted from most level 10-23 Humanoid monsters.Can be looted from Barrel of Milk.Can be purchased for 1 25 from various drink vendors.