Chill a Cocktail glass.
Combine Leopold Gin, simple syrup and grapefruit bitters in a mixing glass and set aside.
Rinse the cocktail glass with Green Chartreuse, leaving a small puddle in the glass.
Now, add ice to the tumbler and stir and strain the mixture into the cocktail glass.
Garnish with a lemon twist.
This recipe requires the specifically named ingredients. Adjust the amount of simple syrup and bitters to taste.
If you can't get Leopold Brothers, I suggest seeking something with a citrus forward profile. Leopold favors orange. See suggestions in the comments
A simple cocktail with Green Chartreuse, built in a manner similar to the Sazerac.