- 2 pounds russet potatoes , peeled and cut into 2-inch chunks
- 2 pounds parsnips , peeled and cut into 2-inch chunks
- 2 cloves garlic , peeled
- 1 Tbsp. salt , plus more to taste
- 1 cup buttermilk
- 3 Tbsp. butter , cut into small pieces
- 4 large, thinly sliced scallions
- Freshly ground pepper
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.