Simmer: Put chicken, peppercorns and bay leaf in a large pot (dutch oven or large high-walled frying pan). Peel garlic cloves, cut a slice into them, and add to pot. (You can use less garlic, but note that garlic powder does not give the same taste or quality.)
Add soy sauce and vinegar to pot: 5 parts soy sauce to 3 part vinegar. (I just tip the bottle and count "glops" as it pours.) Add some water so the pot is about half full; if you're cooking more, then adjust. Important: the liquid should be pretty brown from the soy sauce, rather than very watered down.
Cover; simmer on medium heat for 15-20 minutes, then remove from heat.
Fry: Pour liquid into a bowl and set it aside. (I do this by slightly opening the top of the pot, tipping and pouring into the bowl.)
Pour some cooking oil into the bottom of the pot and brown the chicken at a high heat. (Cover the pot to keep from splattering.) You may have to take some of the chicken out of the pot to do this easily. You can also brown the garlic lightly.
Remove from heat and let the pot cool. This is important — otherwise, the soy sauce can end up with a burnt taste. You may also want to pour out any residual oil, if you are big on fat-free diets.
Boil: When pot has cooled down, pour the sauce back in. Cover, and boil at medium heat for 45 minutes to an hour. Adobo is done when the chicken is cooked and tender.