Servings: Serves 6–8
Ingredients 2 pounds russet potatoes , peeled and cut into 2-inch chunks2 pounds parsnips , peeled and cut into 2-inch chunks2 cloves garlic , peeled1 Tbsp. salt , plus more to taste1 cup buttermilk3 Tbsp. butter , cut into small pieces4 large, thinly sliced scallionsFreshly ground pepper
Put potatoes, parsnips, garlic, and salt into a large pot. Add enough water to cover by 2 inches; bring to a boil. Reduce heat to medium-low and simmer uncovered until vegetables are tender when pierced with a fork, 15 to 20 minutes.
Drain well, then press mixture through a potato ricer or food mill and return to pot; discard any remaining solids. (Alternately, mash well with a potato masher.)
Return pot to stove over low heat. Add buttermilk and butter; cook, stirring often, until butter is melted and mixture is well combined, 2 to 3 minutes. Fold in scallions, then add salt and pepper to taste and cook until hot throughout, 1 to 2 minutes more. Transfer to a large bowl and serve.
Extra idea: When preparing potato mashes and roasts, try mixing in other root vegetables such as celeriac (celery root) or rutabaga.