Place the potatoes and garlic in a pot. Cover with cold water. Season with salt. Bring to a boil and simmer for 25 minutes or until the potatoes are tender and fall apart easily when pierced with a fork. Drain. Return to the pot.
Using a potato masher, purée the potatoes and garlic with the butter. Gradually add the milk and mix until smooth (see note). Season with salt and pepper.
Serve in individual bowls. When ready to serve, add a drizzle of browned butter or a cube of butter, if desired.
If you choose to prepare the mashed potatoes in advance, add a little extra milk to make the mashed potatoes slightly runnier than you normally would. Mashed potatoes tend to thicken up very quickly when not used immediately.