Quarter onions (do not peel). Bring a large pot of water (about 1 1/2 liters or approximately 6 1/3 cups) to a boil. Add onions and sea salt.
Lightly crack the shells of the hard-boiled eggs and place in a jar, along with bay leaves and peppercorns.
Strain onion broth through a sieve over eggs to cover. Let stand at least 2 days before serving.