For the Crust and Topping:
Zest of 2 lemons (I'm not a fan of lemon zest so I used about 2T lemon juice)
1½ cups granulated sugar
3 cups all-purpose flour
¼ teaspoon salt
1½ cups (3 sticks) unsalted butter, cubed and chilled
For the Blackberry Filling:
4 large eggs
2 cups granulated sugar
1 cup sour cream
¾ cup all-purpose flour
Pinch of salt
6 cups fresh blackberries (I used a combination blackberry, strawberry, raspberry mix)
1. Preheat the oven to 350 degrees F. Grease a 9×13-inch baking pan with butter; set aside.
2. In a small bowl, combine the granulated sugar and the lemon zest. Using your fingers, rub the zest into the sugar until all of the sugar has been moistened. In the bowl of a food processor, combine the lemon sugar, all-purpose flour and salt. Pulse a few times to combine. Add the butter and continue to pulse until the pieces of butter are no larger than the size of peas, about 10 to 12 pulses.
3. Measure out 1½ cups of the crumb mixture to use for the topping and put it in the refrigerator until needed. Press the remaining mixture into the bottom of the pan. Bake the crust until golden brown, about 15 to 20 minutes. Let cool for about 10 minutes while you prepare the filling.
4. To make the filling, whisk the eggs in a large bowl. Whisk in the sugar, sour cream, flour and salt until thoroughly combined. Gently fold in the blackberries. Spoon the mixture evenly over the crust and make sure all of the blackberries are in one layer and not sitting on top of one another.
5. Sprinkle the reserved crust mixture evenly over the filling. Bake until the top is lightly browned, about 45 to 55 minutes. Let cool for at least 1 hour before cutting.