1 1/2 oz of Reposado Tequila
1/2 oz of creme de cassis (or blackcurrant-flavored liqueur)
1/2 oz of Lime Juice
2-3 oz of Ginger beer
Combine all ingredients, except ginger beer, and shake. Fine-strain into an ice-filled Collins glass, top with ginger beer and garnish with a lime wedge and fresh blackberry (optional).