Place potatoes and garlic in a large saucepan and cover with cold water. Add salt and bring to a boil. Cook, covered, over medium heat until the potatoes are tender, about 10 minutes. Drain the potatoes and return them to the pan. Shake the pan over low heat to dry the potatoes slightly. Remove the pan from the heat.
Mash the potatoes with a potato masher or an electric mixer (do not use a food processor).
In a sauce pan, bring the chicken broth to boil. Remove from heat and add enough hot broth to the mashed potatoes to make a smooth purée. Stir in sour cream and season with salt, pepper and nutmeg.