Heat oven to 375°F. Butter 9-inch square pan.
In large mixer bowl, beat butter and sugar until well blended. Add milk and egg.
In small bowl, combine flour, baking powder and salt. Add to butter mixture; stir just until combined.
Fold in blueberries. Pour batter into buttered pan.
Combine all Topping ingredients in food processor bowl with metal blade; process until combined. Sprinkle evenly over batter.
Bake at 375°F for 45 to 50 minutes or until toothpick inserted in center comes out clean. Cool 20 to 30 minutes before serving.