In a stockpot or pasta pot, bring about 2 gallons of water to a boil with a palmful of salt and a splash of oil.
Meanwhile, set a large frying pan over high heat, then coat the bottom of the pan with oil. Add the onions with a pinch of salt and cook, working in batches if necessary, until browned, about 2 minutes. Return all the onions to the pan, then turn the heat to medium-low and cover. Continue to cook, stirring frequently, until the onions have turned a deep golden color, about 20 minutes.
Peel the potatoes and cut into 1-inch chunks. When the water has come to a full boil, add the potatoes. Cook, uncovered, until easily pierced with a fork, about 15 minutes. Drain and return to the pot.
Using a potato masher or large whisk, begin to break down the potatoes. Add the sour cream, milk and butter and continue to mash until the desired consistency is reached. Season to taste with salt. Add the caramelized onions and chopped chives and mix well. Place in a large serving bowl and cover with foil to keep warm. Sprinkle with additional chives and crushed potato chips right before serving.