Preheat oven to 400 degrees F. Grease 9-inch round metal pan.
For cake, combine 2 cups biscuit & baking mix with sugar. Add milk and egg, and beat vigorously for 1/2 minute. Spread into cake pan.
For topping, combine 1/2 cup baking mix with brown sugar and cinnamon. Mix in margarine until crumbly. Sprinkle topping over batter.
Bake for 20-25 minutes.