To make the syrup: add ginger, 4 sprigs of rosemary, sugar, and water to a small saucepan. Bring to a boil, and reduce heat to a simmer. Simmer for 3 minutes. Let cool completely, then strain.
To make the drink: rim your glass with blood orange salt. Add tequila, blood orange juice, lime juice, syrup, and triple sec to a cocktail shaker. Add ice and shake until very cold.
Add fresh ice to your blood orange salt-rimmed glass and pour the drink over. Garnish with blood orange slices and rosemary sprigs.
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Notes
*I just massage some blood orange zest into kosher salt!