Electric Milk is a Dairy Food item from the Reign of Giants DLC. It is dropped by killing a Volt Goat that has been charged, i.e. struck by Lightning. Electric Milk can be consumed as it is, or used as an ingredient for recipes in the Crock Pot, such as Ice Cream.
When consumed, it restores 10 , making it a mediocre Sanity-restoring item; this is far lower than the Sanity restored from Ice Cream, a food that needs a dairy item like Electric Milk to create.