Keller’s Skillet Roast Chicken with Root Vegetables

4 to 4 1/2 pound chicken

Kosher salt and freshly ground black pepper

garlic cloves, smashed and peeled (smash with the side of a chef's knife, makes it easier to peel)

thyme sprigs

medium-sized rutabagas (also called "swedes"), ends cut and discarded, rutabagas peeled, and any outer tough layer discarded, then rutabagas cut into 1/4-inch wedges

medium-sized turnips, prepared the same way as the rutabagas

medium-sized carrots, peeled and cut in 2-inch segments

small yellow onion, peeled, roots cut off but core kept intact (see the photos for Frenching onions), other end cut off and discarded, the onion then cut into quarters

small red-skinned new potatoes

About 1/3 cup olive oil

butter, room temperature (spreadable)