Begin by filling a small rocks glass to the rim with ice. Make sure not to skimp on the ice! You’ll be adding hot espresso to the glass in just a minute, so you want enough ice to cool it down quickly.
Pour tonic water and simple syrup over the ice and let it sit.
Prepare 2 ounces of fresh espresso.
Carefully pour the espresso into your rocks glass. If you want a nice, layered look, pour slowly and directly onto an ice cube, or use an upside-down spoon to distribute the espresso over the top of your tonic water without mixing
Add a slice of lemon or orange to your beverage (optional) and serve!