This coffee-flavoured tequila sour is more brown than "Negra" (black) but is a tasty riff on a Margarita. How much agave syrup you should use depends on...
Comments about this being too sour make my head spin, I found this too sweet, and that was with Luxardo Espresso, a much dryer coffee liqueur. That said, this is a delightful, delicious Margarita variant and I really dig it. 2-3 barspoons of agave syrup is what I'll use going forward.