We wash the cherries under a stream of cold water, we sort them (we remove the rotten fruits), we clean them of the tails and we remove the seeds. The fruits thus prepared are put in a larger pan, then covered with sugar and left to cool for a few hours in the cold.
When enough syrup is left, put everything to boil, over low heat, without covering the pot. When the mixture starts to boil, leave more syrup and a foam will form, which we can easily remove with a foamer or a dry spoon.
Boil for about 2 hours, until the amount of syrup is reduced by half and if we take a little syrup with a spoon and let it cool, it will not flow easily from the spoon (the drop sticks to the spoon, it becomes extremely sticky). If the syrup is sufficiently bound, turn off the heat and cover the pan with a towel (no lid, no condensation to form), so that the jam binds even better (during this time the cherries draw their syrup, increasing its volume).
As long as the jam stays "quiet" (10-15 minutes) we prepare the jars: wash them with detergent, rinse them well and dry them in the microwave (until the water drops disappear completely - 2-4 minutes, depending on the number of jars) or in the oven of the stove (placed on a grill or tray - about 20 minutes).
When the jam is still hot, we fill the jars and staple them with new lids, previously kept in boiling water for a few minutes. Before stapling, wipe them well with a napkin, but make sure they are still hot, so that the rubbery part adheres better to the lip of the jar.
Turn the jars with the lids down, cover them with towels or a blanket and leave them like that until the next day or until the jam cools completely.
We label the jars and keep the jam in a dry and cool place for a few years.