Peel and chop the potatoes. Add to a large pot and cover with water and heat over medium high heat. Bring to a boil, add in 1 tsp of the salt. Stir to combine.
Continue to boil the potatoes until fork tender, approximately 20 minutes.
Pour the potatoes into a strainer, draining out the water. Return the potatoes to the pot and place on the burner with the heat off. Stir and allow the potatoes to dry briefly with the remaining heat of the burner.
Preheat the oven to 350 degrees F.
Spray a 3 quart baking dish with non-stick cooking spray and set aside.
Add the butter to the potatoes and allow to melt.
Pour in the milk and sour cream. Mash the potatoes until fairly smooth and creamy.
Add in the white pepper, garlic powder and remaining salt. Taste and adjust seasonings as desired.
Add in 1 and ½ cup of the shredded cheese and mash into the potatoes. Continue until potatoes are mashed to desired consistency.
Spoon the potatoes into the prepared baking dish. Top with the remaining shredded cheese in an even layer.
Bake for 15 minutes until cheese has melted.
Turn the oven to broil on high and bake an additional 4-5 minutes or until top layer of cheese is golden and crispy as desired.
Remove from the oven, allow to cool briefly. Top with chopped chives.