1 1/4 pounds whole peaches
2 tablespoons fresh lemon juice, divided
3/4 pound peeled and cored fresh pineapple
1 1/2 cups sugar
Dip the peaches in boiling water for 30 seconds, then move them to an iced water bath. When cool enough to handle, peel, halve and pit them. Coarsely chop peaches and place them in a heavy, non-reactive 5-quart pan. Stir in 1 tablespoon lemon juice to prevent discoloration.
Coarsely chop the pineapple before combining it with the peaches in the saucepan. Cover and bring fruits to a boil. Uncover and simmer 10 minutes, stirring regularly. After most of the fruit juices evaporate, stir in remaining lemon juice and begin adding the sugar 1/2 cup at a time. Allow jam to return to the simmer between additions. Cook another 5 minutes over medium heat or until the candy thermometer reads 210 degrees.
Fill hot, sterilized jars to within 1/4 inch of lips. Wipe the rims clean, attach new lids and screw the caps on tightly. Invert the jars briefly for a quick vacuum seal, or process in a boiling water bath, submerged by 1 inch, for 10 minutes.