In a mixing bowl, cream together the butter, sugar and egg. In a separate bowl, stir together the flour, baking powder and salt. Then add the milk and flour mixture alternately to the creamed mixture, while beating.
Once combined, gently stir in the blueberries, and pour into a greased and floured 9 inch pan.
For the topping, combine all ingredients, except butter, and then cut in the butter with a pastry blender, or I use two butter knives.
Sprinkle over the top of your batter, and then bake for 45 minutes in a preheated 375 degree oven, or until a knife inserted in the middle comes out dry.