Peel, pit, and dice the fresh peaches. Pour lemon juice into large, heavy-bottomed sauce pan. Add the peaches and stir to coat. The lemon juice keeps the peaches from turning brown.

Pour half the sugar over the peaches and stir gently. I advise doing a taste test before adding the rest of the sugar. Depending on the sweetness of the peaches you're using, you may need less or more sugar than 1 cup. If desired, add the rest of the sugar. Let the mixture sit for 30 minutes.

Bring the peach mixture to a boil over medium high heat, stirring occasionally. Reduce the heat, add cinnamon and stir (you can add more cinnamon, if desired). Let the peach mixture simmer for an hour or longer until the liquid has become thick like jelly.

Halfway through the cooking process, use a potato masher to crush the peaches just slightly. You want to leave a few chunks in the jam for that extra burst of flavor when eating.

When your jam has reached a desired consistency, turn off the heat and pour mixture into sterilized jelly jars, leaving one-fourth inch at the top. Wipe the top of the jars with a paper towel and screw the lids on top until just hand tight.

Place the filled jars into a large pot of water. The water should cover the jars by about one-half inch. Bring the water to a rolling boil and process for about 15 minutes. Turn off the heat and remove the jars with tongs. Let cool for 12-24 hours. You might hear a popping sound as the jars seal.

After cooling, check the seal by pushing down on the center of the lid - it shouldn't move at all. You can transfer your peach jam to the cupboard. If any of the lids do move, place in the refrigerator and use within a couple months.