Preheat oven to 375 degrees. Grease and flour 9x13-inch baking dish. Set aside. In bowl cream together butter and sugar. Beat in eggs. Add milk. In small bowl mash 1/2 cup blueberries then add to egg mixture. Add flour, baking powder, salt and vanilla. Mix well. Carefully stir in remaining blueberries. Pour into baking dish. Sprinkle with sugar. Bake for 30 minutes or until firm.