If there are peaches and blueberries at your farmers market right now (or your grocery store), you might want to introduce them to each other. Then you can make this out of them. I happen to prefer blueberries to blackberries so made a substitution and improved upon the recipe.
I took the whole pan to work without even cutting into them to see if they were ok first. They were. They were very, very, very, okay. Excuse the plastic utensil and plate but I just snapped this photo at my desk so you could see what it looks like out of the pan.
It's really more of a cobbler/cake than it is a bar which I think of as something you can pick up and eat like a brownie. Excellent for breakfast. Not overly sweet and packed with fruit.