Make hibiscus syrup: Boil water and sugar until sugar dissolves. Add hibiscus flowers and simmer for 10 minutes. Strain and cool.
Salt rim the glass with a mixture of salt and crushed dried hibiscus flowers if desired.
Add mint leaves to shaker and muddle gently to release oils.
Pour in tequila, lime juice, and hibiscus syrup.
Fill shaker with ice and shake vigorously for 15 seconds.
Double strain into prepared glass filled with fresh ice.
Garnish with a mint sprig.
Notes
Store hibiscus syrup in an airtight container in the refrigerator for up to 2 weeks.Fresh lime juice works best - avoid bottled alternatives.For a spicier version, add 2-3 thin jalapeño slices during muddling.The cocktail can be made virgin by replacing tequila with sparkling water.