Topping. In small mixing bowl, combine topping ingredients. Blend with fork until crumbly. Set aside.
Sift 1 1/2 cups sifted flour with baking powder and salt into a bowl. In a medium bowl, beat together beaten egg and 3/4 cup sugar and 1/3 cup melted butter. Add milk and vanilla. Stir in flour mixture and mix well.
Pour batter into a greased and floured 8-inch square or 9-inch layer-cake pan. Sprinkle topping crumb mixture evenly over batter. Bake at 375Â° 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.