Cut 6 of the lemons in quarters lengthways, but not all the way to the top, so that they still hold together (do this over a bowl to preserve any juice).
Squeeze the 6 other lemons and reserve the juice.
Put a good tablespoon of salt in the bottom of each sterilised jar, then pack the quartered lemons with salt and push them tightly together into the jars.
Divide the bay leaves, peppercorns and coriander seeds, if using, between the jars and cover with the squeezed lemon juice and remaining salt.
If the juice doesn't cover the lemons then top up with water.
Close the jars and shake. Make sure that there is a layer of salt at the bottom. Every day for 2 weeks turn the jars and add salt if necessary.
They are ready to use after about a month but the longer you leave them, the better they taste.
They will keep for up to a year if stored in a cool, dark place.