Technique
Fill a large wine glass with ice, add the Prosecco first, then Aperol, and finish with soda water. This order helps preserve bubbles and lets the denser aperitivo mix as it falls; one gentle stir is enough.
The Aperol Spritz is an Italian wine-based cocktail, commonly served as an aperitivo. It consists of Prosecco, Aperol, and soda water.

TonicDB editorial guide
The familiar 3:2:1 Spritz structure is easy to remember: three parts sparkling wine, two parts bitter aperitivo, and a small soda finish. Large ice and cold ingredients keep it bright, lightly bitter, and lower in intensity than a spirit-forward cocktail.
Fill a large wine glass with ice, add the Prosecco first, then Aperol, and finish with soda water. This order helps preserve bubbles and lets the denser aperitivo mix as it falls; one gentle stir is enough.
Use a large stemmed glass with an orange half-wheel tucked inside the bowl. Serve it as soon as it is built, ideally with all three ingredients chilled so the ice cools the drink without doing all the work.
Small or insufficient ice melts quickly and makes the spritz taste watery. Vigorous stirring and repeatedly topping the glass destroy carbonation. Avoid adding syrup—the combination is already sweetened by the aperitivo and wine.
For a lighter drink, add a little more soda rather than reducing the ice. For a drier impression, choose a brut sparkling wine and raise it slightly above three parts while keeping the Aperol at two.
These notes explain how to execute and adapt the recipe shown above. Ingredients and serving traditions vary, so taste and adjust thoughtfully.
Contributed by @alfg