This simple soup is far greater than the sum of its parts. It keeps well for a few days in the fridge and, like the rest of us, even improves with a night’s rest. Reheat gently.
To a heavy 5-quart pot, add the potatoes, onions, carrots, water, salt, thyme, bay leaf and nutmeg. Bring to a boil over high heat. Cover and reduce heat to maintain a simmer. Simmer, stirring occasionally, until all vegetables are very tender, about an hour.
Remove thyme stems and bay leaf. Pass soup through a food mill with a medium disc attached. Almost all of the solids should go through. (Or use a stick blender for a less rustic texture.) Stir in cream or olive oil. Add pepper and additional salt, if desired, to taste. Return to pot and reheat over low heat before serving.