1. Peel, pit, and cut peaches into 1/2-inch chunks. Combine with 1/4 cup water in a large saucepan; bring to a simmer. With a potato masher, mash into a coarse puree. Simmer, stirring often, 10 minutes.

2. Stir in sugar until dissolved. Bring to a boil; reduce heat, and simmer, stirring often, about 15 minutes. (Test doneness by spooning some jam onto a plate; when you run your finger through it, a trail should stay for a few seconds.)

3. Skim foam from surface; stir in fresh lemon juice. Let cool.