Place a small ceramic plate in the freezer. Place 2 cups of blueberries in a high-sided saucepan, and mash with a potato masher. Add the remaining blueberries along with the rest of the ingredients. Set the saucepan over medium-high heat, and bring mixture to a boil.
Once the blueberries start boiling vigorously enough that the bubbles don't dissipate when you stir, set the timer for 12 minutes and continue boiling the berries at the same rate, stirring frequently.
When the jam begins to thicken, pull the plate from the freezer and place a small amount of the jam on the plate. Run your finger through the jam, and if it jells and seems thick, remove the pan from the heat. If the jam is not thick enough, place the plate back into the freezer, and continue to cook the jam for a minute or two longer. Test again. Repeat until the jam is thickened (I usually have to cook mine for an additional 10 minutes to get it to the right consistency).
Divide the jam into clean glass jars. Allow to cool for about 2 hours, then top with lids. When the jam cools to room temperature, store in the refrigerator and enjoy within 2 weeks.
Notes
The original author of this recipe shared that getting jam to jell can be a funny business. If for some reason your jam doesn't thicken, remove it from heat and tell everyone it's blueberry sauce. For the record: mine turns out just perfect.