Wash and scrub potatoes. Peel and dice into 1-inch chunks and place into a 5-quart pot. Cover with water, add 2 teaspoons of salt and bring to a boil over medium-high heat.
Reduce the heat to medium-low and simmer for 15-20 minutes, or until potatoes are fork tender.
Meanwhile, place milk and butter in a small saucepan over medium heat. Warm until the butter is completely melted - do not boil. Set aside.
Once potatoes are tender, drain and return to the pot. Mash several times until mostly smooth (some lumps are ok).
Stir in butter mixture, sour cream, garlic powder, pepper, cheeses, bacon and chives. Reserve some cheese, bacon and chives for topping. Taste and add salt as desired.
Transfer to a serving bowl and top with the reserved cheese, bacon and chives. Serve immediately.
Storage - Leftovers can be stored in an airtight container in the fridge for up to 4 days.Reheating - Leftovers can be reheated in the oven for 15-20 minutes at 350℉ until warmed. Or in the microwave for 30-60 seconds.