Cut top and root end from onions. Peel and rinse. Make two cuts into each onion without going all the way through, making quarters that stay together. Core the middle of the onion.
Place each onion in the middle of a foil square large enough to securely wrap the onion. Put 1/4 tsp of beef boullion granules into the middle of each onion. Crush about a 1/4 tsp of rosemary on to the top of each onion. Top with 1 Tbs of butter. Add salt and pepper to taste.
Securely wrap each onion. I double wrap so juices don't leak out. Place on medium grill for 30-40 minutes until soft when squeezed.