4 large russet potatoes, peeled and quartered
4 medium or large carrots, peeled and diced into half-inch pieces
2 yellow onions, diced
1 tablespoon kosher salt
½ cup cream or milk
¼ cup butter (half a stick), cut into small pieces and at room temperature
Salt and pepper to taste
1 tablespoon fresh parsley or chives, finely chopped, to garnish
Place the cut potatoes, carrots and onions in a large stock pot and fill with water, covering the vegetables by at least an inch of water. Add 1 tablespoon of kosher salt. Cook over high heat until a rolling boil is achieved, then reduce to medium heat and simmer until the potatoes are fork tender and starting to fall apart, about 20 to 25 minutes.
Remove from heat and drain the water. Return the vegetables to the pot and cook over medium heat, stirring occasionally, until the moisture has mostly evaporated, about 3 to 5 minutes.
Use a potato masher or large wooden spoon to mash the vegetables together until well combined, but still somewhat chunky. Add the butter and use the masher to incorporate it into the potato mixture.
Slowly add the cream, starting with a ¼ cup, and use a wooden spoon or rubber spatula to stir it into the potatoes until well combined. Add more cream if mixture is too thick and stir aggressively until incorporated. Taste and add salt and pepper as desired.
Transfer mashed potatoes to a serving dish, garnish with fresh parsley and/or chives and serve.
This dish may be made at least 2 days in advance and reheated before serving, or frozen for 2 to 3 months in an airtight container.