In a large pot, add the cubed potatoes, garlic, and cold water to cover the potatoes with an inch above.
Add about 1 tablespoon of salt to the pot and bring to a boil.
Boil the potatoes for 10 to 15 minutes or until fork-tender.
Drain the potatoes and return them to the pot. Turn the heat to low and let them sit for 1 to 2 minutes.
While they're cooking, prepare the butter mixture by heating the butter, milk, and remaining salt until warm.
Add the cooked potatoes to a bowl or mix them right in the pot.
Using a potato masher, mash the potatoes carefully, avoiding overmixing.
Pour in the butter mixture and fold into the potatoes.
Fold in the cream cheese and sour cream and adjust seasoning with salt and pepper.
Serve warm with pats of butter and chives if desired.
