Ingredients

• 1 medium parsnip (1/4 lb), peeled and cut crosswise into 1-inch pieces
• 1 large Yukon Gold potato (1/2 lb), peeled and cut into 2-inch pieces
• 1 1/2 teaspoons salt
• 2 teaspoons unsalted butter

Instructions

1. Cover parsnip and potato with cold water by 1 inch in a 3-quart saucepan, then add salt and bring to a boil, partially covered. Reduce heat and simmer vegetables, partially covered, until very tender, 10 to 15 minutes.
2. Reserve 1/4 cup cooking water, then drain vegetables in a colander. Return vegetables to pan and coarsely mash with a potato masher or a fork, discarding any tough core from parsnip if necessary. Stir in butter, 2 tablespoons reserved cooking water, and salt and pepper to taste. Thin with additional cooking water if desired.