1. Peel, core, and dice the apples. (Be sure to chop the fruit into small chunks, about 1/4 to 1/2 inch cubes, as they'll remain close to that size in the finished jam.)

2. Toss the chopped apples in lemon juice and sugar, cover, and refrigerate for overnight (12 to 24 hours). This step is important, and at an absolute minimum, they need 4 hours, preferably more. Macerating the fruit in sugar helps it retain a chunky texture, rather than turn into applesauce.

3. Prepare a water bath canner (if canning, skip for a freezer jam).

4.Place the apple mixture into a heavy-bottomed saucepan and bring to a boil over high heat. The mixture will foam, so be sure your pan is big enough to handle foaming to avoid overflows.

5. Stir apple/sugar mixture occasionally, watching for overflows, and cook for about 20-30 minutes.
If apple pieces are too large, crush slightly with a potato masher (optional).

6. Cook until the apple jam reaches gel stage, using an instant-read thermometer or testing a small amount on a plate placed in the freezer. (Gel stage is 220 degrees F at sea level and a bit below that at higher elevations.  The finished temperature drops by 1 degree for every 500 feet above sea level.  I'm at 1000 feet, so my jams finish at 218 F.)

7. Once the jam reaches gel stage, immediately remove it from the heat and pack it into jars leaving
1/4 inch headspace, and seal with 2 part canning lids

8. Store the apple jam in the refrigerator for immediate use, or process in a water bath canner for 10 minutes. Turn off the canner and allow the jars to sit an additional 5 minutes before removing them to a towel on the counter. Check for seals after a few hours, and store any unsealed jars in the refrigerator.