Hasselback Sweet Potatoes With Garlic-Yogurt Sauce

Position rack in bottom of oven; preheat to 425°F. Line a large rimmed baking sheet with parchment paper.

Cut off and discard about ¼ inch from top of garlic head, exposing the cloves. Place the garlic head on a piece of foil and drizzle with 1 teaspoon oil. Wrap completely with foil. Transfer to the prepared baking sheet.

Make crosswise cuts every 1/8-inch along each sweet potato (see Tip, above), slicing almost to the bottom but not all the way through; place on the baking sheet with the garlic. Mix together cumin, 1/2 teaspoon salt, cayenne and the remaining 3 tablespoons oil in a small bowl. Brush the oil mixture onto the sweet potatoes until they're completely covered, then drizzle any of the remaining oil into the cuts. Roast until the garlic is soft, about 30 minutes. Transfer the garlic to a clean cutting board to cool. Continue roasting the sweet potatoes until the insides are tender and the outsides are crispy, about 20 to 25 minutes more.

Squeeze the garlic cloves from their skins into a small bowl. Add yogurt, parsley, pepper and the remaining 1/8 teaspoon salt; mix, mashing the garlic cloves, until well combined. Serve the sauce with the sweet potatoes. Garnish with parsley and/or lemon zest, if desired.