How to Make It
Place potatoes, half-and-half, and 2 teaspoons salt in a large saucepan. Bring to a boil over medium-high. Reduce heat to low, partially cover, and cook, stirring often, until potatoes are tender when pierced with a fork, 20 to 22 minutes. Remove from heat and transfer mixture to a large heatproof bowl.
Working in batches and using a slotted spoon, transfer potatoes to a potato ricer and rice over the saucepan. Reserve cooking liquid in bowl (you should have about 1½ to 2 cups). Stir butter and remaining 3 teaspoons salt into mashed potatoes. Fold in sour cream and enough cooking liquid to reach desired consistency. Reserve any leftover cooking liquid for reheating.
Note: Reheat mashed potatoes in a saucepan over medium, stirring often, adding about ¼ cup cooking liquid to thin if needed.