re-hydrate dried and salted cod with water and milk
Normally I poach the fish in milk as a last stage of preparation, especially if I'm making brandade.  The milk, in that case, adds creamyness to the fish. both making up for some of its residual dryness as well as helping mask the salty taste.  However, that's after the fish is soaked in water for 24-48 hours.  A 1-hour poach in milk is also my way of &quot;emergency quick soaking&quot; cod.
Presumably soaking it in milk would be to achieve the same effect, without poaching it.  Salted cod has almost no fat, so the milk bath would be adding some much-needed fat to it.