Prepare agave syrup by diluting agave nectar with water in 1 : 1 ratio. Grate a piece of ginger and squeeze the juice out. Measure 0.25 oz of ginger juice in a bar jigger. Fill a tall glass with large chunks of ice.
In a Boston shaker, muddle together all the ingredients except tequila to release the flavors. Then add Arrogante Blanco tequila and a handful of ice and shake vigorously for 10 to 15 seconds. Strain the cocktail through a fine mesh strainer into the prepared cocktail glass to remove pulp and seeds.
Garnish the cocktail with blackberries.
Mat Biancaniello (Eat Your Drink)