[mfjordvald]

You're misunderstanding the terms a bit. Salting is only done once because it's a random string you apply to the users password so that if two users use the same password they do not result in the same hash. This is primarily meant to combat pre-generated rainbow tables and forcing each password to be broken individually.

You're thinking of multiple rounds of hashing, designed to increase the computation cost of the hashing. For example Bcrypt has a built in cost factor. While this is definitely important it's not quite the same as salting.