1/2 pound Yukon gold potatoes, peeled and quartered
1/2 to 1 cup heavy cream, heated
4 tablespoons cold unsalted butter, cut into pieces
Place the chestnuts in a large saucepot and fill with water. Season generously with salt and bring the pot to a boil. Add the potatoes and continue to boil until the potatoes are fork-tender, 20 to 25 minutes.
Drain the cooked potato-chestnut mixture and return to the pot. Add the hot cream and cold butter and stir vigorously until combined. Check the seasoning; add salt, if needed. If the mixture is a little stiff, add more cream and butter until it reaches the desired consistency. Place in a serving bowl and cover with foil until ready to serve.