Wash the potatoes thoroughly under cold running water, scrubbing away any dirt. Peel approximately 60% of the skin from each potato, leaving about 40% for texture, color, and flavor. Cut the potatoes into even pieces, about 1 to 2 inches each, to ensure uniform cooking.
Place the potatoes in a large pot and cover with cold water by about 1 inch. Add a generous amount of salt to the water (about 1 tablespoon per quart). Bring to a boil over high heat. Reduce the heat to maintain a steady boil until the potatoes are tender and easily pierced with a fork, about 15 to 20 minutes.
Drain the potatoes in a colander and let them sit for 2 to 3 minutes to allow excess moisture to evaporate. This step is important for achieving the right texture.
Return the drained potatoes to the pot or transfer to a large mixing bowl. Mash the potatoes, leaving some small lumps for texture if preferred.
Add the butter and mix until melted and incorporated. Gradually add the heavy cream and mix gently until you achieve your preferred consistency. Season with salt. Taste and adjust the seasoning as needed.