Heat the oven to 350 degrees.
Beat together the sugar butter and lemon zest in a mixer until light and fluffy.
Mix in the egg and vanilla until smooth.
Stir together the salt, 1 ¾ cups of the flour and baking powder in a bowl.
Alternate mixing in the dry ingredients and the buttermilk until well combined.
Place the blueberries in a bowl, and toss them in the remaining flour.
Fold the coated blueberries into the batter.
Spread the mixture into a well greased 9x9 baking dish, and sprinkle it with sugar on top.
Bake for 40 minutes, or until completely cooked through.