Step 1

Place a rack in the upper third of the oven and preheat oven to 375 degrees F.

Step 2

Cut the tops off of each onion, but leave most of the skins on the onion.

Step 3

Arrange the onions in a square baking dish or a rimmed sheet pan.

Step 4

Drizzle the olive oil over the onions. Place a thin pat of butter on each onion.

Step 5

Sprinkle generously with salt and pepper and top with a rosemary sprig.

Step 6

Bake for 25 minutes until bubbling and tender.

Step 7

Increase the oven temperature to 400 degrees F and cook for another 15 to 20 minutes until the onions are completely tender and the tops are browned.

Step 8

Remove from the oven and allow to cool slightly.

Step 9

Remove the skins, slice and enjoy warm.