Peel the potatoes and cut them into quarters, then transfer them to a large pot filled with cold salted water. If including garlic, add the cloves and bring the water to a boil. Cook uncovered for about 15 minutes, or until the potatoes are tender when pierced with a fork. Thoroughly drain the potatoes.
While the potatoes are draining, heat the milk or cream until warm, either on the stovetop or in the microwave.
Return the drained potatoes to the warm pot or a mixing bowl. Add the melted butter and begin mashing. Gradually incorporate the heated milk while mashing, adjusting the amount to achieve your preferred texture.
Season generously with salt and freshly ground black pepper. Serve immediately while hot.