Add Small Cucumber (1), Fresh Basil Leaf (4), Lime Juice (1 fluid ounce), and Cointreau (1 fluid ounce) to shaker.
Muddle, then add White Mezcal (2 fluid ounce) and St~Germain (0.5 fluid ounce). Shake for 20 seconds.
Salt rim and strain margarita into glass.
Add shaved ice (or one cube of ice). Garnish with basil and lime.