Prepare a canner (large canning pot) with insert and jars. Cover with water and bring to a rolling boil for 5 minutes to sanitize jars. Leave in water until ready to use.
Place new liners and snap lids in a bowl of HOT tap water.
Peel and dice the peaches.
With a potato masher, mash the fruit in a single layer at a time, until you have exactly 4 cups of mashed peaches.
Stir in the freshly squeezed lemon juice and pectin.
Put in a large pot and bring to a boil on high.
Add in the 4 cups of sugar.
Boil for 1 minute.
Remove from heat, stirring and skimming off any foam for 5 minutes.
Pour or ladle into sterilized jars, until ¼" from the top.
Place new snap lids on top and tighten threads until finger tight.
Once filled, place back in the canner, making sure the jars are covered by an inch of water and boil, covered for 10 minutes.
Remove onto a kitchen towel and leave undisturbed to set for 24 hours.
Press the centre of the lids to make sure they are sealed, if any pop back up, store in fridge.
Any leftover jam can be eaten immediately or stored covered in the fridge for up to week.
Notes
The peaches do not need to be mashed into full puree, some chunkier pieces are fine and rather desirable.
This is a small recipe, that results in 6 jars of jam. It is easily doubled.
Recipe by Pretty Petunias at https://www.prettypetunias.com/peach-jam/