I fail to remember where this recipe first appeared but chances are it was from Canadian Living magazine. This simple dish is much richer than you would expect and pairs well with grilled meats especially lamb and pork. Since sweet potatoes are very moist, adjust the amount of sour cream or milk to your taste. I do recall that the original recipe recommended placing the sweet potatoes and onion mixture in a food processor until blended. I found this method too gluey and altered it as stated.