Mashed Potatoes with Herbs

Bring milk with parsley and chives to a simmer in a saucepan, then remove from heat. Let stand, covered, 20 minutes. While milk is standing, cover potatoes with salted cold water by 2 inches in a large pot and simmer, uncovered, until very tender, 20 to 30 minutes. Drain in a colander and, when just cool enough to handle, peel. Preheat oven to 350 °F. Mash warm potatoes with a potato masher, gradually adding 1 1/2 cups herbed milk. Add remaining milk 1/4 cup at a time, mashing, until potatoes reach desired consistency. Season with sea salt and pepper, then transfer to an ovenproof serving dish. Heat potatoes, covered, in middle of oven 15 minutes. (If making potatoes to go with lamb, you can heat potatoes while lamb stands.) Serve potatoes hot, topped with pats of butter.