Trim a slice from the top of each onion, and peel the onion without cutting off the root end. With a potato peeler, cut a small cone-shaped section from the center of the onion. Cut the onions into quarters from the top down, stopping within a half inch of the root end.
Place a bouillon cube in the center, slip slivers of butter in between the sections and sprinkle with pepper. Wrap each onion in a double thickness of heavy-duty foil.
Place the onions directly onto the hot coals and cook for 45 minutes, turning every so often. These can also be baked in a preheated 350 degree F oven for 45 minutes, but I still say they're better grilled over charcoal. Serve in individual bowls because the onions produce a lot of broth, which tastes like French onion soup.