You can prepare this low-cal cocktail in 2 minutes, says Emilie Yount, editor of Recipe4Living.com. For one serving, you’ll need: three or four mint leaves, a lime wedge, 1 oz. white rum, diet lemon-lime soda (such as Sprite Zero, Diet Sierra Mist, or Diet 7-Up), ice, and sugar (just for the rim of the glass!).
To prepare: Muddle mint leaves with white rum and the juice from lime wedge (1/8 of the lime). Muddling is done by lightly crushing the mint (just until the leaves bruise) using a mortar and pestle or whatever you have on hand. Just don't shred the mint!
Run the squeezed lime wedge around the rim of the glass, and then dip the top of the glass in a shallow plate of granulated sugar to coat the rim. Pour the muddled mixture into your glass, fill with crushed ice, and top off with the diet soda.