Final answer:
A perfect shot of espresso has a balanced flavor, strong aroma, and thick crema. Accurate measurements with regard to water and coffee is crucial. The Viennese specialty also includes whipped cream and powdered sugar served separately.
Step-by-step explanation:
The qualities of a perfect shot of espresso include a strong, balanced flavor profile, a robust aroma, and a thick, persisting crema on top. It should be brewed with the right ratio of water to coffee, typically using 4 cups of water and 3 scoops of coffee, which involves precise measurements. A perfect shot of espresso should also have a rich, dark color, yet not taste burnt or too bitter. Although espresso serves as the base for various drinks, if we consider the Viennese specialty described, it involves serving strong black coffee in a glass, crowning it with whipped cream and providing powdered sugar separately, which may add sweetness as per individual preference.