1. Beat margarine and sugars.
2. Add rest of ingredients (excluding melted chocolate), one at a time.
3. Spread batter into a nine- by 13-inch pan and bake at 350 degrees Fahrenheit for about 45 minutes or until lightly browned. (Check for doneness with a skewer.)
4. When cooled, drizzle with melted chocolate, if desired, and cut into small squares.