topping:
1/2 cup brown sugar
1/4 cup sifted all-purpose flour (sift before measuring)
1/4 cup butter, room temperature
1 teaspoon cinnamon

cake:
1 1/2 cups sifted all-purpose flour (sift before measuring)
2 1/2 teaspoons baking powder
1 teaspoon cinnamon
1/2 teaspoon salt
1 egg, beaten
3/4 cup sugar
1/3 cup melted butter
1/2 cup milk
1 teaspoon vanilla extract

Topping: In small mixing bowl, combine topping ingredients.
Blend with fork until crumbly. Set aside.

Cake: Sift 1 1/2 cups flour with baking powder, cinnamon, and 
salt into a bowl. In a medium bowl, beat together egg and 3/4 cup 
sugar and 1/3 cup melted butter. Add milk and vanilla. Stir in 
flour mixture; 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 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.