Cherry preserves

Rinse the cherries thoroughly, pat dry and remove the stem, then cut each cherry in half. Transfer the cherries in a bowl, add the sugar, lemon zest and 3 tablespoons of lemon juice and set aside for at least 6 hours or overnight in a cool, dry place or in the refrigerator. Discard the lemon zest, transfer the fruit in a pan and cook over medium heat for about an hour, stirring occasionally. The cherry preserves will be ready when a drop poured on a tilted plate will not run down but will remain firm and smooth. Pour the preserves in sterilized glass jars while still boiling hot, filling the jars up to 1/2-1 inch from the rim. Clean the rim thoroughly and put the lids on, sealing the jars tightly. In order to create a vacuum seal, put the jars upside-down on a warm surface and let aside for 5-10 minutes, then invert and let cool.