. Preheat the oven to 375 degrees Fahrenheit (190 C). Prepare a 9×13 casserole dish with cooking spray and put it aside.
. Bring a big saucepan of water to a boil, then add your potatoes. Cook potatoes till tender with a fork (about 8 minutes).
. Return the potatoes to the saucepan after draining them.
. To the saucepan, add the butter, sour cream, milk, parsley, garlic powder, salt, and pepper. Mix until thoroughly combined and the butter has melted.