1 sweet (like Vidalia) onion per serving

Preheat the oven to 400 degrees.

Clean the onion(s) off with a damp cloth so you don't dislodge the papery skin.

Cover a baking sheet with a piece of foil, which you should crumple so the onions will stand up on it. Put the onions on the foil root side down. Place the pan in the middle level of the oven, and bake until the onions are soft throughout when pricked deeply with a cake tester or skewer.

Slit the tops, and place a pat of butter in each. To eat, scoop the warm buttery flesh out of the surrounding skin like you do when eating a baked potato (except don't eat the onion skin).