Preheat the oven to 350 degrees F. Butter the bottom and sides of a 9X13 inch metal baking pan. Put a long piece of parchment paper in the bottom of the pan, letting the parchment extend up two sides of the pan and overhang slightly on both ends. Place another piece of parchment paper in the same manner, perpendicular to the first sheet. (This will make it easy to remove the bars from the pan after they have baked.)

In a small bowl, combine sugar and zest. Rub the zest and sugar between your fingers (Rubbing the zest into the sugar will release oils from the zest and create a lemon scented sugar). Transfer sugar mixture to a food processor fitted with the metal blade. Add flour and salt and pulse until combined, about two 1-second pulses.

Add the butter and toss with a fork to cover in flour mixture. Pulse until pieces of butter are no larger than the size of peas, about 10 to 12 pulses. Set aside 1 ½ cups of the crust mixture and place in the refrigerator until ready to use.

Press the remaining mixture into the bottom of the prepared pan. Bake until golden brown, about 12 to 15 minutes. Let cool for 10 minutes while you make the filling.

To make the filling: Whisk the eggs in a large bowl. Add the sugar, sour cream, flour and salt. Gently fold in the berries. Spoon the mixture evenly over the crust. Sprinkle evenly with the reserved crust mixture.

Bake until the top is lightly browned, about 45 to 55 minutes. Cool for at least 1 hour before slicing.