For the tart shell:

1. Preheat oven to 400 degrees.
2. Butter a 12-inch tart pan.
3. Place all the ingredients in the bowl of a food processor fitted with the metal blade. Pulse until the mixture resembles coarse breadcrumbs. Use longer pulses until the dough forms a ball. 
4. Wrap the dough in plastic wrap and refrigerate it until ready to use. (You can make the dough ahead of time and remove it from the fridge 20 minutes before using.)
5. On a lightly floured board, roll out the dough to a 14-inch circle, ¼-inch thick. Line the tart pan with the dough. Trim the edges with a sharp knife and then prick the dough with a fork. 
6. Line the tart shell with parchment paper and fill with pie weights or dried beans. Bake for 20 minutes until just golden. Remove the pie weights and parchment paper and return the tart shell to the oven to bake for 5 more minutes. The shell should be golden brown. Remove from the oven and let cool on a wire rack.

For the quick jam:

1. Place all of the ingredients (including the lemon rinds) in a medium saucepan over medium heat. 
2. Cook for 10-13 minutes, skimming off any foam that forms. The jam is ready when it thickens enough to coat the back of a spoon.

To assemble the tart:
2 lbs cherries — pitted
1 lb blueberries

1. Combine the cherries, blueberries and jam in a large bowl. Pour the jam filling into the prepared tart shell and top with the fresh fruit.