Prep: Peel the onion. Cut off the top stem, but leave the root end intact.
Core: Use a knife to cut a cone-shaped hole in the top center of the onion (about 1 inch deep).
Stuff: Place the butter and the bouillon cube inside the hole. Sprinkle with salt and pepper.
Wrap: Place the onion on a sheet of foil. Wrap tightly and seal the top so no liquid can escape.
Boil: Place in a pot. Add water until it reaches halfway up the side of the onion. Cover and boil/simmer for 45–60 minutes.
Serve: Remove with tongs. Carefully open foil (watch for steam). Spoon juices over the onion and serve warm.