Watermelon Ginger Margarita

2 oz Espolon tequila
3/4 oz fresh lime juice
1/2 oz ginger syrup
4 1-inch cubes watermelon

Muddle the watermelon cubes in the bottom of a shaker. Add ice and all the ingredients. Shake until well chilled. Strain into a double old fashioned glass with a salted rim and an ice sphere.