Roasting garlic and thyme in olive oil infuses them with a heady flavor that makes a luxurious addition to these mashed potatoes. Purple potatoes make a delightful lavender mash, but you can use white potatoes if you prefer.
2 pounds purple or all-purpose white potatoes, cut into 1-inch pieces
1/2 cup reduced-fat sour cream
1/2 cup low-fat milk
1/2 teaspoon salt
1/4 teaspoon freshly ground pepper, or to taste
Preheat oven to 400 °F.
Rub off excess papery skin from garlic head without separating the cloves. Slice the tip off the head, exposing the cloves. Place the garlic in a small baking dish, such as a bread pan. Drizzle with oil and lay thyme sprigs around it. Cover with foil. Roast until very soft, 30 to 45 minutes. Uncover and let cool.
About 15 minutes before the garlic is done, cook potatoes in a pot of boiling water until tender, 8 to 12 minutes. Drain well.
Return the potatoes to the pot. Squeeze the garlic cloves out of their skins into the potatoes. Strain the oil through a fine sieve over the potatoes, pressing on the solids (discard the thyme). Add sour cream, milk, salt and pepper; mash to desired consistency.
Make Ahead Tip: Cover and refrigerate the roasted garlic (Step 2) in an airtight container for up to 3 days.