In a small bowl, cream butter and sugar until light and fluffy. Beat in egg. Combine the flour, baking powder and salt; gradually add to creamed mixture alternately with milk, beating well after each addition. Fold in blueberries. Spread into an 8x4-in. loaf pan coated with cooking spray.
For topping, combine the flour, sugar and cinnamon in a small bowl. Cut in butter until mixture resembles coarse crumbs. Sprinkle over batter.
Bake at 350° for 40-45 minutes or until a toothpick inserted in the center comes out clean. Cool for 10 minutes before removing from pan to a wire rack.