Cook garlic in hot oil in a Dutch oven over medium heat, stirring occasionally, 3 minutes. Add 6 cups water and next 3 ingredients; bring to a boil. Reduce heat; cover and cook 20 minutes or until tender.
Drain potatoes; return to Dutch oven. Cook, stirring constantly, over medium heat 30 seconds. Remove from heat.
Add buttermilk and remaining ingredients; mash with a large fork to desired consistency.