Clean garlic, chop cloves into halves. Stick garlic inside meat holes. As much as possible. If your meat doesn't have enough holes, you can make deep ones, using a knife.
Place meat inside plastic box and cover tight with lid. Chop onion into 12 pieces. Place onion all around meat. Cover meat and store in fridge for at least 24 hours. I always do 2 days.
Remove meat from container. Remove as much of garlic as u can from meat. Place meat on a ceramic cooking sheet. Cook in preheated oven at 475 degrees for 15 minutes, until it brown. Making meat brown on outside right away, will keep meat juicy through cooking process.
Lower heat to 350F, bake for another 30-40 minutes. Remove from oven, slice and serve hot. It taste the best when it's fresh out of oven.