Place the sweet potatoes in a pot and cover with cold water. Bring the potatoes to a boil over high heat. Reduce the heat and simmer about 20 to 30 minutes, until the potatoes are done. Check by piercing with a fork; there should be no resistance. Drain well.
Mash the sweet potatoes with a potato masher or fork, or use a food mill.
Add the lime juice and stir well. Add the milk and stir. Add Cajun seasoning, to taste.