Turn the heat to medium low, and stirring every 5 minutes or so, let the fruit cook. It will first get juicy with the fruit intact, and then the fruit will start to disintegrate. As it cooks, there will be foam on top, but just keep stirring, don’t worry about skimming it.
If you want to jazz up the flavor, you can add chipotle chiles in adobo, cloves, a cinnamon stick, or a vanilla bean while it cooks. The key, that I’ve learned, is to not over cook it. But if you do, and the next day you find that you have a jar of rock-hard candy instead of jam, all is not lost! You can place the jar into a pot of water and let it come to a boil. The jam will heat up and become liquid, and then you can slowly add more water to it until it’s more runny. Try the freezer test again and then repack it. (This is how I eventually saved my sour-cherry jam).
Apricot jam | www.homesicktexan.com