Cut the top 1/4 off of the garlic heads so that the tops of the cloves are exposed. Place them on a baking sheet and drizzle them well with olive oil.
Preheat oven to 350°, cook garlic for about 40 minutes or until you see that the garlic cloves have browned, and the head itself is soft. Remove and let cool for handling.
Wash chicken and place in baking pan breast up.
With the handle of a wooden spoon, or anything that will slide without tearing the skin, separate the skin from the meat starting at the lower breast, and taking your time until you have loosened all the skin that you can reach.
Make a small cut in the skin on top of the drumsticks, and insert the spoon into the cut, loosening all the skin on the legs and thighs.
Gently squeeze all the garlic heads into a blender, the cloves will be soft and will slide out of the shell easily.
Add the juice from half the lemon, the rosemary, and black pepper.
Turn the blender on low and after mixture is working, slowly drizzle the olive oil into the mixture. Stop when mixture is mixed.
Using either your fingers, a pastry bag, or however you can do it, (I just use my fingers and a spoon) insert about half of the mixture under the chicken skin and then gently press down on it to spread it around evenly under the skin.
Place onion and lemon inside the chicken, tie legs together, wipe the outside lightly with olive oil and sprinkle with Emeril's essence to taste.
Bake in preheated oven at 350° for about 50 minutes or until almost done and the outside is browning nicely.
Remove chicken and spread the remaining mixture over the chicken to cover.
Return to oven and cook until the surface is browned and the chicken is tender.