Grease an 8-inch, heat-resistant, non-metallic cake pan.
Preheat a conventional broiler.
Cream butter and the 3/4 cup sugar together in a large bowl until fluffy. Beat in egg.
Sift the flour, baking powder and salt together.
Add flour mixture and milk to the sugar mixture alternately, beginning and ending with flour mixture.
Pour into prepared cake pan. Spread evenly. Combine the 1/2 cup sugar and cinnamon in a small bowl and sprinkle over the batter.
Heat, uncovered, in Microwave Oven 6 minutes.
Insert a wooden toothpick to test for doneness.
Place cake in a conventional oven 4 inches away from heating element of the broiler unit for a few minutes or until topping is browned.