Preheat oven to 375° degrees F. Spray 12-muffin tin with vegetable spray. In a large bowl sift together the flour, baking powder, and salt and set aside. In another large bowl, cream together 2/3 cup sugar, butter, zest and egg until fluffy. Using a rubber spatula, fold in the flour mixture alternating with the milk. Fold in the blueberries. Be careful not to over mix the batter. Spoon batter evenly into muffin tin. Sprinkle tops with sugar. Bake until golden brown for about 25 minutes. Cool muffins in tin.