Peel outer layers of onion and slice off a section of one end of each onion (about 1/4 of onion) With a spoon scoop out a hole in the middle of each onion.
Place bouillon cube in hole and add some butter.
Replace top of onion and wrap in heavy foil.
With a closed grill cook for 1 hour or until tender.
Cut into bite size chunks and pour juices over top.