To make syrup: Place Blood Orange (1 cup) and Granulated Sugar (3/4 cup) over medium heat. Bring to a bubble for 1-2 minutes. Turn off the heat and let cool while you make the cocktail.
Rub half of glass rim with a slice of Blood Orange Syrup (3 tablespoon). Dip in Salt (to taste).
Fill glass with Ice (to taste). Combine freshly squeezed blood orange juice, blood orange syrup, juice from Lime (1/2) and White Mezcal (1/4 cup) in a shaker. Shake for 20 seconds. Pour over Ice ( to taste).
Top off with Club Soda (to taste).
Garnish with blood orange slice.