Sterilize jars - I used the oven method (wash in hot soapy water then place face down on a lined baking sheet in the oven at 225f for at least 15 minutes or until ready to use) and prepare water bath canner by filling with water deep enough to cover jars by an inch.
Meanwhile, bring a large pot of hot water to a boil and prepare an ice bath. Once the water is boiling rapidly drop the peaches into it for 45 - 60 seconds, then quickly remove with a slotted spoon into the ice bath. At this point the skin should just slide off, if not, use a pairing knife to help with the sticky spots.
Place the peeled peaches in a bowl filled with cold water and a healthy squirt of lemon juice until you're ready to cut them.
Drain the pot used to peel the peaches, and wash out. Cut peaches in halve lengthwise and remove the pit, then coarsely chop and add to pot, dump sugar on top.
Remove jars from oven one at a time, and ladle hot jam into them. If adding flavourings, do so in the middle of ladling. I had small containers and I used them to contain my flavours until I was ready to use them, then dumped into jars as required. Fill each jar leaving 1/4" head space.
Place a new, warm lid on top and tighten the ring finger tight. Using jar gripper, gently lower jars into water bath and process for 25 minutes.
Using jar gripper, carefully remove the jars keeping them upright and place in a safe spot for 24 hours without touching. After 24 hours have passed, you can check the seal on each of the jars, if you can press down on the lid and hear an audible pop, the jar has not sealed - place that one in the fridge and eat it first.