Chive and Parsley Mashed Potatoes

For chive and parsley oil

• 1 cup chopped fresh chives
• 3/4 cup chopped fresh flat-leaf parsley
• 1/2 cup plus 3 tablespoons olive oil
• 1/4 teaspoon salt

For mashed potatoes

• 5 lb yellow-fleshed potatoes such as Yukon Gold
• 1 1/2 cups milk
• 1 stick (1/2 cup) unsalted butter, cut into tablespoon pieces
• 1 1/4 teaspoons salt
• 3/4 teaspoon black pepper

Preparation:

Make oil:

Purée chives and parsley with oil and salt in a blender until smooth. Pour herb oil through a fine-mesh sieve into a glass measure, pressing on and discarding solids.

Prepare potatoes:
Peel and quarter potatoes. Cover potatoes with salted cold water by 1 inch in a 5-quart heavy pot, then simmer, uncovered, until very tender, about 25 minutes.

While potatoes are simmering, bring milk, butter, salt, and pepper just to a simmer, stirring until butter is melted.

Drain potatoes in a colander and return to pot. Add hot milk mixture and mash with a potato masher until almost smooth, then stir in 4 tablespoons herb oil.

If desired, serve potatoes drizzled with some of remaining oil.

Cooks' notes:Oil can be made 4 days ahead and chilled, covered. Bring to room temperature before using.

Potatoes can be made 1 day ahead and chilled, covered. Bring to room temperature before reheating in a microwave or double boiler, stirring occasionally.