Wash and dry the peaches. (Tip: It is best to use just-ripe peaches.)
Blanch the peaches; this will make them easier to peel later. Using a sharp knife, cut a shallow ‘X’ into the bottom of each peach. Boil a large pot of water; submerge the peaches for about 1 minute.
Transfer peaches immediately into an ice water bath, for about 1 minute. Drain.
Peel off the skins; they should come off fairly easily. Discard skins.
Slice the peaches in half. Remove and discard the pits.
Chop the pitted peaches into smaller chunks.
Place peach chunks in a large (nonreactive) pot over medium-low heat.
Zest and juice the lemons. Add lemon zest and juice to the pot with the peaches. Stir to combine.
Cook for about 15 minutes, until the peaches are soft, and the juices are released. Stir frequently, using a wooden spoon to break them down slightly.
Add the sugar; stir until dissolved.
Increase heat to medium-high. Bring to a simmer for 5 minutes, stirring continuously. Check for consistency—jam is ready when the mixture is thick enough to leave a trail behind the spoon. If it needs more time to thicken, reduce heat to medium-low and continue cooking for another 30-45 minutes.
Transfer jam to cleaned and sanitized mason jars. Seal with lids and bands; allow to cool. Note: jars should self-seal (or “pop”) as the mixture cools. Once cooled, check that jars are sealed by attempting to push down on the center of the lid. (If you can’t press down then they have sealed properly.)
Store or refrigerate until ready to serve.
(Note: refrigerate any jars that did not properly seal and use these first. Alternately, you can seal them using a hot water bath canning method.)
Serve homemade jam with Martin’s Old-Fashioned Real Butter Bread.