Combine the potatoes, 1/2 teaspoon salt, and enough water to cover by 1 inch in a medium saucepan. Bring to a boil and cook until just fork-tender, about 12 minutes. Remove from the heat and drain. Return to the pan and cook for 1 minute, mashing with a potato masher or heavy whisk over medium heat. Add the cream, butter, remaining 1/4 teaspoon salt, and white pepper and mash until smooth. Stir in the parsley.
Remove from the heat and spread on a plate to cool. (The potatoes can be made in advance and refrigerated until ready to use.)
Makes about 2 1/2 cups