Cut your five lemons into thin slices. Then, quarter the slices and transfer to a bowl.
Add in the sea salt and cinnamon sticks. Stir to combine.
Scoop the lemons into a clean, wide-mouth, quart-size Mason jar. Smoosh the lemons down gently with a wooden spoon to help them release some of their juices and to help them all fit in the jar.
Combine the whey and the juice of the last two lemons. Pour this over the top of the lemons until the liquid reaches an inch below the top of the jar.
Cover the top of the jar with plastic wrap (I like to push it down slightly over the lemons to help keep them under the liquid). Screw on your lid and band.
Leave the lemons out on your counter for 2 weeks, giving the jar a quick turn upside down each day. During this time, the lemons will develop lactic acid and all sorts of beneficial bacteria. You can read more about the benefits of lacto-fermentation here.
After this two week period, transfer the lemons to your refrigerator where you can enjoy them for months to come.