Pit fresh 3 lbs sour cherries. If working with pitted fruit, the total weight should be about 2 1/2 lbs pitted, or roughly 5 cups pitted fruit.
Place the fruit in a heavy-bottomed jam pot along with lemon juice. Bring to a boil over medium-high heat.
Cook the cherry mixture, stirring continuously to avoid boil-overs, for about 20 minutes until the fruit has completely fallen apart.
Add sugar. (If adding pectin, now is the time, see notes).
Continue cooking the jam until it reaches gel stage, about 25 to 30 more minutes.
Test for gel stage on a plate that's been placed in the freezer, or with an instant-read thermometer (220 degrees F at sea level).
Turn off heat and ladle jam into prepared jars. De-bubble, wipe rims and adjust headspace to 1/4 inch. Store in the refrigerator for immediate use (within 1 month), or process in a water bath canner for 10 minutes for a shelf-stable jam.
