Preheat your oven to 350 degrees. Grease a 9x13 inch pan and set aside. In a medium sized mixing bowl, cream together the butter, lemon zest, and sugar. Add the egg and vanilla and beat until combined.
In a separate mixing bowl, whisk together the 1 and 3/4 cup flour, salt and baking powder. Toss the blueberries in the remaining 1/4 cup flour.
Add the flour mixture to the creamed mixture a little at a time alternating with the buttermilk until combined. Gently fold in the blueberries.
Spread the batter into the prepared baking pan. Sprinkle with coarse sugar. Bake for 35-40 minutes or until it is cooked through and toothpick is clean. Let rest for 15 minutes before serving.