Wash your canning jars thoroughly and set aside. Blanch fresh peaches in boiling water for 30–45 seconds, then plunge into an ice bath. Peel skins, chop peaches, and mix with 1 cup sugar.

In a large pot, combine chopped peaches, lemon juice, and butter over medium-high heat. Cook until bubbling, about 10 minutes, stirring occasionally.

Measure out the powdered pectin and remaining sugar in separate bowls. Gradually stir pectin into the simmering fruit mixture after it reaches a full boil. Boil for 1–2 minutes until thickened.

Once boiling, add the remaining sugar and stir continuously. Cook for 1 minute to ensure sugar dissolves completely.

Test the jam's consistency by placing a spoon in the freezer for a few minutes. Dip it into the jam; a clean line should remain visible.

Fill prepared jars with hot peach jam, leaving 1/4" to 1/2" headspace. Wipe rims, seal with lids, and process in a boiling water canner for at least 10 minutes.

Allow jars to cool undisturbed for 24 hours. Check seals before storing in a cool, dark place.