Add Aperol, gin, lemon juice, and simple syrup to an empty cocktail shaker. Shake hard for at least 30 seconds to 1 minute until a nice froth forms.
Add ice and shake again to chill the mixture.
Strain into a chilled coupe glass*. Garnish with a dried citrus slice.
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notes
*To chill your coupe glass, add it to the freezer for about 20 minutes before serving the cocktail. You can also fill the glass with ice while you make the cocktail and dump the ice before straining the cocktail in.