Preheat the oven to 350 degrees F. Spray an 8x8-inch baking dish with cooking spray. Set aside.

In a medium bowl, combine the graham cracker crumbs, melted butter, sugar, and pinch of salt. Stir until graham cracker crumbs are moist. Press crumbs firmly into prepared pan. Bake the graham cracker crust for 10 minutes. Remove from oven and allow to cool to room temperature.

Meanwhile, combine the egg yolks and condensed milk in a medium bowl. Stir in the lime zest and lime juice. Stir until mixture is smooth and begins to slightly thicken.

Pour the lime filling evenly over the graham cracker crust. Place the blackberries evenly into the lime filling, pushing them down a little. Bake for 15 minutes, or until just set.

 Cool to room temperature, then chill in the refrigerator for at least one hour before serving. Cut into squares and serve.

Note-Bars will keep covered in the refrigerator for 3-4 days.