Place the potato quarters in a large pot and cover them with cold water. Bring to a boil over high heat, then reduce the heat to medium.
Cook for 12–15 minutes, or until the potatoes are easily pierced with a fork. Drain well and return them to a large mixing or serving bowl.
While the potatoes are still hot, add the butter, sour cream, milk, minced garlic, garlic powder, salt, and pepper.
Mash everything together using a potato masher or fork. For a rustic texture, stop when the potatoes are mostly combined but still a little chunky.
For a creamier consistency, continue mashing until smooth. If the mixture seems too thick, add a splash more milk until you reach your preferred texture.
Adjust seasoning to your liking. Transfer to a serving bowl, sprinkle with fresh herbs, and serve warm.