Build the ingredients in a rocks or wine glass, over ice, and add the garnish.
Note: Aperol is the most widely available bitter liqueur; it is also the sweetest. If you prefer a more bracingly bitter spritz, try splitting Aperol with Campari (1:1). And if you can find them, Contratto Aperitif, Contratto Bitter, Mauro Vergano Americano, and Cappelletti Aperitivo Americano are four aperitivo bitters we find ourselves returning to over and over again in this classic formula.
Reprinted with permission from Spritz: Italy’s Most Iconic Aperitivo Cocktail, with Recipes, by Talia Baiocchi and Leslie Pariseau, copyright © 2016. Published by Ten Speed Press, an imprint of Penguin Random House LLC.