In a mixing bowl, cream butter and sugar. Beat eggs and vanilla. Combine the flour, baking powder and salt; add to creamed mixture alternately with milk. Fold in blueberries. Pour into a greased 13in. X 9in. X 2in. baking pan.
For topping, combine sugar and cinnamon. Cut in butter until mixture resembles coarse crumbs. Sprinkle over batter. Bake at 375 degrees F for 35-40 minutes or until a toothpick comes out clean. Cool in pan on a wire rack.