Place quartered potatoes in a large stockpot or Dutch oven. Fill with water just enough that the potatoes are completely covered. Set over high heat, bring to a boil.
Reduce to medium heat, slightly cover, and allow to simmer for 20-25 minutes or until fork-tender.
Drain potatoes really well to ensure no water is left. Transfer potatoes to the bowl of a stand mixer. Using the whisk attachment, mash the potatoes gently, them place on stand with the whisk attached.
With mixing speed on low, slowly pour in milk, then add butter one tablespoon at a time. Add salt, pepper, and garlic powder. Increase speed to medium and whip for 10 seconds.
Top with fresh chives, if desired. Serve immediately.