For the crust and topping:
Zest of two lemons
1 1/2 cups sugar
3 cups all-purpose flour
1/2 teaspoon salt
1 1/2 cups chilled butter (3 sticks), cut into cubes
For the berry filling:
4 large eggs
2 cups sugar
1 cup sour cream (I used 1/2 cup sour cream, 1/2 cup nonfat Greek yogurt )
3/4 cup all-purpose flour
A pinch of salt
6 cups fresh berries, such as blueberries or a combination of berries, or frozen berries (be sure to thaw and drain first)
Preheat the oven to 350°F. Grease a jelly roll pan with cooking spray. Zest the two lemons. Combine the lemon zest, sugar, flour, salt and butter in an electric mixer fit with a paddle attachment. Beat the ingredients on medium speed until the mixture looks dry and crumbly.
Reserve 1 1/2 cups of the crust mixture to use as the topping. Press the remaining mixture into the bottom of the pan (you will really have to work at it, but it will evenly cover the bottom of the pan). Bake the crust for 12-15 minutes, until it is golden brown. 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 (and yogurt, if using), flour and salt. Gently fold in the berries. Spoon the mixture evenly over the crust. You may have to distribute the berries evenly around.
Sprinkle the reserved crust mixture evenly over the filling. Bake for 45-55 minutes, until the top is lightly browned. Cool for 1 hour before slicing. Store the bars in the refrigerator.