Place potatoes in a large pot or dutch oven. Add enough water to cover the potatoes. Stir in 1 teaspoon of the kosher salt. Bring to a boil, then reduce heat, cover and simmer about 20 to 25 minutes.
Meanwhile, place the remaining 1/2 teaspoon kosher salt, pepper, garlic powder, sour cream, Parmesan cheese and butter in the bowl of an electric mixer.
When potatoes pierce easily with a paring knife, remove from heat and drain. Add potatoes to the bowl with the other ingredients and mix on medium speed until mostly smooth (there may be some lumps, but we usually don't mind that). Serve.