Place the cubed potatoes in a large pot and cover with cold water. Add a pinch of salt and bring to a boil over high heat.
Reduce heat to medium-low and simmer for 20–25 minutes, or until potatoes are fork-tender.
While the potatoes cook, melt the butter in a small saucepan over low heat. Add the minced garlic and warm the milk until steaming (do not boil).
Drain the cooked potatoes thoroughly and return them to the hot pot. Let sit for 1 minute to dry out slightly.
Using a potato masher or hand mixer, mash the potatoes until smooth. Gradually add the warm butter, milk, and cream (if using), mixing until creamy and well combined.
Season with salt and pepper to taste. Serve immediately while hot.
Notes
For extra fluffiness, avoid overworking the potatoes after mashing.