Grease 12-cup muffin pan. Preheat oven to 375 degrees. In large bowl with mixer on medium speed, cream butter or margarine and sugar until light and fluffy, add eggs, one at a time, beating well after each addition. Combine flour, baking powder and salt. Ad alternately to creamed mixture with milk and vanilla. Crush 1/2 cup blueberries and add to batter. Folding remaining berries into batter and sppon into muffin pan. Sprinkle with sugar. Bake 30 minutes. Cool in pan for 5 minutes and turn onto wire rack.