I love David Lebovitz's recipe for "No Recipe Jam"- it's really brilliant.
Here's a link to his recipe in its entirety, I have the summed up version below: http://www.davidlebovitz.com/2005/06/norecipe-yikes/
The results are out of this world. The difference between homemade and store-bought jams is so obvious, and so amazingly delicious. You should try it at least once. And there's no better fruit to make jam with than sour cherries!
Rinse the cherries under cold water. Remove the stems and pits from the cherries.
My gorgeous assistant pitting the cherries for me by hand as I catch up on my tv shows!
Here's how to pit the cherries: Gently tear open a tiny part of the cherry.
Remove the pit while leaving the cherry intact
Place the cherries, and zest from 1-2 lemons in a large pot.
Bring to a boil over medium-high heat
Squeeze the juice from 1-2 lemons over the cherries
Continue to boil until very bubbly, stirring throughout. Careful not to burn.
Add 1-2 cups of sugar over, and stir in. Allow the jam to simmer over Medium-High heat until it thickens, about 20- 25 minutes. Place in jars, and allow to cool before placing the lids over.