Low Sugar Natural Pectin Jam - cooking recipe

Ingredients

8 8 cups plums (could experiment with other fruits) or 8 cups nectarines (could experiment with other fruits)
1 cup sugar, divided (you might even be able to use less, but try it this way the first time)
2 medium granny smith apples (use only Granny Smith type for maximum pectin content)
2 tablespoons lemon juice, fresh or bottled

Preparation

Place a small saucer in the freezer to chill for later testing of jam thickness. In large deep heavy skillet (preferably NOT non-stick), or your widest heavy-bottom sauce pan, sprinkle cleaned berries or other sliced fruit with 3/4 cup of the sugar. Mash coarsely and let sit 15 minutes to \"juice\".
Bring fruit mixture to a boil over medium-high heat, stirring occasionally. Boil 15 minutes - hard enough to bubble but not splatter, stirring occasionally & skimming any foam off.
Meanwhile, peel, core & grate apples.
Stir in apples, lemon juice & remaining 1/4 cup sugar & keep boiling, stirring more often now & scraping bottom of pan to prevent sticking.
Cook this way until thickened, about 20-45 more minutes (depends on ripeness of fruit, altitude, etc).
Test by placing a small drop of jam on the chilled plate from the freezer and let it sit a minute; when properly thickened, the jam should not run at all when plate is tilted at a steep angle.
If not thick enough, let it cook longer -- it will get there eventually!
Ladle hot jam into half-pint canning jars (they're heat-proof) and put the lids on hand-tight. Because this jam has less sugar, it's best to use half-pint (1 cup) or smaller jars, because it may spoil quicker once opened. You can either store the jars as-is in the freezer once cooled, or you may can them by submerging hot jars immediately in boiling water for 10 minutes.
If you don't have canning jars, let jam cool in the covered pan until room temperature. Ladle into plastic or other containers (1 cup volume each or smaller), and store in freezer.