Preheat oven to 325°F.
Lightly grease and flour an 8-inch springform pan. Set aside.
Set aside ⅓ cup of blueberries to put on top of batter before baking, if desired. In a medium mixing bowl, toss the remaining blueberries with 2 tablespoons flour and set aside. Make sure your berries are dry.
In a small bowl combine 2 cups of flour, salt, and baking powder.
In the bowl of a stand mixer combine the butter, lemon zest and ¾ cup of sugar. Beat for several minutes, scraping down the sides as needed, until light and fluffy.
Beat in the egg and vanilla just until incorporated.
Add ⅓ of the flour mixture to the creamed butter and sugar. Beat on low until incorporated. Add ⅓ of the buttermilk and blend until smooth. Repeat adding 1/2 of the remaining flour, then ½ of the remaining buttermilk until both are incorporated, repeat one more time. Remove the bowl from the mixer. The batter will be very thick.
Gently fold in the floured blueberries and any extra flour into the batter using a rubber spatula. Take care not to rupture the blueberries.
Scoop the batter into the prepared pan and spread evenly. Scatter the remaining 1/3 cup of blueberries on top. Sprinkle with the coarse sugar. Bake in a 325°F preheated oven for 50-60 minutes or until the top is lightly browned and a toothpick inserted in the center comes out almost clean.
Allow the cake to rest for 30-minutes before removing the sides of the pan. Serve warm or at room temperature. Refrigerate leftovers for longer storage. The warm cake will crumble a little more than a cooled cake but it's absolutely delicious.