Prepare a small boiling water bath canner and 3 half pint jars.

Combine the peaches and sugar in a 12-inch nonreactive skillet and stir until the sugar dissolves and the peaches look juicy.

Place the skillet on the stove over high heat and bring to a boil. Once the jam starts bubbling, reduce the heat to medium-high.

Cook, stirring regularly, until the jam thickens. You know it's done when you can pull the spatula through the jam and the liquid doesn't immediately rush in to fill the space.

Add the lemon juice and cinnamon, if using. Stir to combine.

Remove the jam from the heat and stir for a few beats, to help the fruit release the last of the moisture.

Funnel the jam into the prepared jars. Wipe the rims, apply lids and rings, and process in a boiling water bath canner for 10 minutes.

When time is up, remove jars from the canner and set them on a folded kitchen towel to cool.