Topping - In small mixing bowl, combine topping ingredients. Blend with fork until crumbly. Set aside.
Sift 1 ½ cups sifted flour with baking powder and salt into a bowl. In a medium bowl, beat together beaten egg and ¾ cup sugar and ⅓ cup melted butter.Add milk and vanilla. Stir in flour mixture and mix well.
Pour ½ the batter into a greased and floured 8-inch square or 9-inch layer-cake pan. Sprinkle with blueberries and top with remaining batter.
Sprinkle topping crumb mixture evenly over batter. Bake at 375° for 25 to 30 minutes, or until cake tests done. Partially cool in pan on wire rack. Cut coffee cake into squares while still warm.
