In a large saucepan or bowl, stir together the peaches and sugar then cover and refrigerate overnight. (12-24 hours is best.)
Sterilize your jars by either boiling in a water bath or by washing and drying in an oven at 210 degrees Fahrenheit for 20 minutes. Boil your lids for 5 mins and leave in the water until ready to use.
Place a small plate in your freezer. This will be used to test your jam.
Heat the peaches and lemon juice over medium-high heat until it just comes to a boil and drop it down to a simmer, stirring to keep it from burning.
At this point you can add in your cinnamon and stir it in well.
Once most of the liquid has cooked off (about 20 minutes in) you can use an immersion blender to get it to the consistency you prefer. (or use a blender if that's what you have, just allow to cool first!)
Return your fruit back to your pan and continue to cook, stirring every now and then.
When your jam is getting glossy and has slightly darkened, transfer a small spoonful to your small plate from the freezer. Allow it to sit about 1 minute then tilt the plate. If the jam runs like liquid down the plate it isn't ready. When it runs slowly down the plate in a "sheet" your jam is good to go. Please note that during this test you should remove the rest of the jam off the heat.
Add your vanilla and stir in well.
Transfer your jam to the jar(s) using a glass measuring cup and a funnel leaving about 1/4″ space.
Screw the lids on but do not over-tighten then process in a boiling water bath if you intend to store the jam before consuming. If you intend to consume right away simply store in your fridge after it has cooled to room temperature.