In a small shallow dish, combine the salt, rosemary, and cayenne pepper. Pour the lime juice into a separate small dish. Dip each glass upside down into the lime juice and then into the salt mixture, set aside.

Strain the blood orange juice with a fine mesh sieve into a large pitcher. Add the lime juice, tequila, triple sec and simple syrup (if using). Give it a good stir until evenly combined.

Fill each of the rimmed glasses with ice and then divide the margarita mix evenly among each glass. Garnish with a blood orange slice and a small sprig of rosemary. Enjoy!