Place onions, lemons, garlic, and bay leaves in a cheesecloth bag. Place bag in a small amount of water in a large stockpot. Stir in salt and pepper. Place over medium heat, and cook 30 minutes.
Add additional water to accommodate crayfish. Bring to a boil; add crayfish, maintaining boiling point of water. Boil, uncovered, 7 minutes. Remove cheesecloth bag; discard. Drain crayfish; peel and eat immediately.