Prep. Wash the jars with hot, soapy water. Place them in a water bath canner and fill it with water so the jars are fully submerged. Set over medium heat and allow the jars to simmer. Place the lids and rings in a saucepan over medium-low heat and simmer. Do not boil.
Cook peaches. Add the peaches, lemon juice, fruit fresh, and cinnamon to a large 6-8 quart pot. Place over medium-high heat and stir all of the ingredients so they’re well combined.
Add pectin. Add the pectin and stir to combine. Bring the mixture to a full rolling boil so that the mixture cannot be stirred down. (Please note that using unripe peaches will not produce enough liquid for this to happen. Make sure you’re using soft, ripe peaches for this recipe.)
Add sugar. Add sugar and stir to combine. Continue to stir the mixture and bring it back to a full rolling boil. Add the butter (if using) to help reduce foam.
Boil. Once the mixture comes to a full rolling boil, set a timer for 1 minute, stirring constantly. Remove from the heat.
Fill jars. Using a canning funnel and ladle, ladle the hot preserves into the hot jars, allowing ½ inch headspace.
Wipe rims and fasten lids. Wipe the rims with a clean, moist towel. (Use a paper towel with some vinegar to help remove any jam from the rims.) Place the lids and rings, tightening so they’re fingertip tight.
Process. Transfer the jars to the water bath canner, making sure the jars are fully submerged with at least 1 inch of water over them. Set to high heat, cover, and bring to a boil. Once boiling, set a timer for 10 minutes.
Rest. Remove the canner from the heat, remove the lid, and allow the jars to sit for 5 minutes.
Cool and check seals. Remove the jars from the canner and transfer them to a heat-safe place. Allow them to cool for 12-24 hours. After 24 hours, check the jars for a proper seal. Once a proper seal is confirmed, you can remove the rings and store the jars in a cool, dark place for up to 18 months or per the lid manufacturer’s recommendations.