Preheat the oven to 325°F. Lightly grease a 9-inch spring-form or square baking pan, and set aside.
In a medium mixing bowl, whisk together the flour, salt, baking powder, baking soda, and sugar. Set aside
In a mixing bowl of a stand mixer fitted with a paddle attachment beat the eggs until blended. Add the sour cream, vanilla, and lemon juice. Mix until blended. Slowly add the melted butter mixing constantly until combined. Add the flour sugar mixture to the sour cream mixture slowly. Mix until the dry ingredients are moistened. The batter will be very thick.
Fold in 1 1/2 cups of blackberries into the batter. Pour it into the prepared pan, and smooth with an offset spatula. Top with all remaining blackberries, pressing the berries slightly into the batter.
Allow the cake to rest for 10 to 15 minutes before baking. If you are using coarse sugar sprinkle it on top, mostly on the exposed batter avoiding the berries.
Bake at 325°F for 60 to 70 minutes or until a toothpick or knife inserted into the center comes out with no wet batter. Moist crumbs are okay.
Cool the cake for 20 minutes, then remove the sides of the springform pan. Slide the cake onto a serving platter or plate. Serve slightly warm or at room temperature. Dust with powdered sugar, or a dollop of whipped cream.
If using a square cake pan, serve straight from the pan.
