Gently muddle mint leaves with simple syrup in a cocktail shaker. This releases the mint oils without breaking the leaves.
Add tequila, lime juice, and ice to the shaker. Shake for 10-15 seconds until well chilled.
Double strain into a Collins glass filled with fresh ice. This keeps small mint pieces from getting into the drink.
Top with club soda and stir gently with a bar spoon. Add about 2 oz of club soda, or to taste.
Garnish with a lime wheel and fresh mint sprig.
Notes
Use 100% agave silver tequila for the best results. Lower quality tequilas can make the drink taste harsh.Make simple syrup by mixing equal parts sugar and hot water until dissolved. Let it cool before using.Fresh lime juice makes a big difference. Avoid bottled lime juice for the best taste.The drink can be made less sweet by reducing the simple syrup to ½ oz.Mint leaves should be fresh and bright green. Brown or wilted leaves will give off bitter flavors.