In large pot, simmer chopped tomatoes, sugar, and lemon juice for about 30 minutes. Add chopped apples, and continue simmering for another 30 minutes or so to evaporate as much juice as you can.
Pour into sterile jam jars. Process in a water bath for 10 minutes for half-pint jars.
Consult the USDA’s Complete Home Guide to Home Canning for the latest information on food safety. It is available for free online from the National Center for Home Food Preservation.