In a large pot place cubed potatoes and fill with water to about 2 inches above potatoes.
Bring to a boil over medium high heat and cook for about 15-18 minutes or until potatoes are just tender.
While the potatoes are boiling, pour the milk into a small pot and add rosemary sprigs.
Over medium heat bring the milk to a low boil (to avoid scalding) and reduce heat to a simmer. As it simmers, the rosemary will infuse the milk.
Drain potatoes and place into a mixing bowl.
Add in cubed butter, chopped roasted garlic, salt and pepper.
Start mixing on medium speed and slowly add in milk until you reach desired consistency. You may not need to use all of the milk until the potatoes are smooth and creamy.