Sterilize jars and lids in a boiling water bath for 10 minutes, then keep warm in a low oven set to 200°F.

Blanch whole peaches in boiling water for 30-60 seconds, then transfer to an ice bath to cool.

Peel, pit, and finely chop the peaches until you have about 4 cups.

Mix chopped peaches, lemon juice, and Sure-Jell in a large pot. Heat over medium-high until a full rolling boil.

Add all the sugar at once, stirring until dissolved. Boil for 1 minute until the mixture thickens.

Ladle the hot peach jam into jars, leaving ¼-inch headspace. Wipe rims and seal with lids.

Process jars in a boiling water bath for 10 minutes. Ensure the water covers jars by at least an inch.

Let jars cool undisturbed for 12-24 hours, then check seals by pressing the center of lids.