Cut the top of each onion. Using a vegetable peeler, knife or your fingers, peel the paper skins from the onions, leaving root ends intact.
Core onions, being careful not to cut into the roots - you need the root intact to hold the onion together. Place each onion on a square of heavy-duty aluminum foil. Drizzle each with 1 tablespoon olive oil.
Place a bouillon cube in the center of each onion and top with 1 teaspoon butter. Wrap onions with the foil and grill on a very hot gas or charcoal grill over indirect heat about 35-40 minutes.
You can substitute butter-flavored cooking spray for the butter to cut fat and calories. You also can cut the measurement for the olive oil down to 1 teaspoon per onion, if desired.
You can also bake these onions in a conventional 350 degrees F oven.