Combine cream, water, potatoes, 1-tablespoon kosher salt and 1-teaspoon black pepper in a large saucepan, set over medium heat.
Bring just to a boil, reduce heat to low and simmer 15-25 minutes or until potatoes are fork-tender.
Drain potatoes in a colander set over a medium, heatproof bowl (reserve the potato milk/water).
Return the potatoes to the pan and set the heat to medium-low. Stir gently until the excess moisture evaporates from the potatoes, about 1 minute.
Add the butter, 1½ teaspoons kosher salt and ½ teaspoon black pepper. Mash the potatoes until smooth and creamy (or fluffadding some of the reserved potato milk-water, when/if necessary. (NOTE: If not serving the potatoes immediately, save about 1-cup of the milk-water to add before serving. Be sure to add the milk-water in ¼-cup increments to ensure the potatoes stay fluffy. No one likes watery mashed potatoes.)
Transfer potatoes to a serving bowl, dot with 3-4 tabs of butter (or drizzle with melted butteand garnish with parsley or cheese, if desired.