1. Use a pestle to crush the basil leaves with the lemon juice and zest in a shaker.
2. Add the other ingredients and shake well. Pour immediately into a cocktail glass and garnish with a slice of lemon.

Variation:
For an alcohol-free cocktail, replace the gin and lemon liqueur with sparkling water and add 5 mL (1 tsp.) of lemon juice and a pinch of sugar.

Source:
Recipe adapted from Je cuisine italien by Stefano Faita, published by Éditions du Trécarré.