Preheat the oven to 350 degrees F. Spray a 13" x 9" baking dish with cooking spray.

In a large bowl, stir together the flour, granulated sugar, and salt. Add the butter and stir until a shortbread-like dough comes together. Press half of the dough into the bottom of the baking dish.

In another bowl, whisk together the eggs, half-and-half, brown sugar, cornstarch, vanilla, cinnamon, and salt. Gently fold in the blueberries and peaches. Pour the mixture over the crust and spread evenly. Crumble the rest of the dough over the blueberry mixture. Bake for 40 to 45 minutes, or until the bars are set and no longer jiggly. Cool completely before slicing into squares.