In a large bowl, cream together the butter, 1 1/4 cups sugar and salt until light and fluffy. Beat in the eggs one at a time. Mix together 1 3/4 cup of the flour and baking powder. Beat in the flour mixture alternately with the buttermilk, mixing just until incorporated. Crush 1/4 of the blueberries, and stir into the batter. Mix the rest of the whole blueberries with the remaining 1/4 cup of the flour, and fold into the batter. Scoop into muffin cups. Sprinkle tops lightly with sugar.