Put the potatoes in a large pot and add enough cold water to cover. Add a few pinches of salt and bring to a boil. Lower to a simmer and cook, stirring occasionally, until the potatoes are tender but not falling apart.
Strain the potatoes and add them back to the hot pot along with the cream, butter and a good amount of salt. Mash well with a potato masher or wooden spoon. If you like garlic, grate in about 1/2 clove and mix well. Taste and adjust the seasoning. Serve warm.
Substitute celery root for potatoes to mix things up.