I bought an 11lb pail of pitted, unsweetened sour cherries this summer, at the peak of the season.  They were still fresh, so I quickly portioned them into 3 cup containers for future use.  It's my turn to make church snack this week, so I pulled a container out of the freezer and hit Google for a simple bar recipe.  I found the following on on several sites, so I don't know who to give credit to.  But I'm hoping that it turns out, because it's a very easy recipe (with a food processor).

CRUST:
1 1/2 c. flour
1/2 c. cold butter
1/4 tsp. salt
5 tbsp. powdered sugar

Mix together well, either in a food processor or by cutting in by hand.  Don't get the crust mixture too warm or it will be sticky and hard to handle. 
Pat into a 9 x 13-inch pan.  Bake for 15 minutes at 350 F.

FILLING:
3 eggs
1 c. sugar
1 c. brown sugar
1 tsp. baking powder
1/2 c. flour
3 c. tart cherries (thawed and drained if frozen)

If using a food processor pour into work bowl and process until well mixed.  Add the cherries and pulse to incorporate, but don't pulverize them into oblivion. You could chop them by hand and fold them into the mix too.

Pour over the partially baked crust and bake for another 45 minutes.