Combine mezcal, overproof white rum, falernum, maraschino liqueur, fresh lime juice, and simple syrup in a cocktail shaker.
Add the egg white and dry shake (without ice) vigorously for 10–15 seconds to emulsify.
Add ice and shake again vigorously for a further 10–15 seconds until well chilled.
Double-strain into a chilled cocktail glass for a clean up presentation, or strain over fresh ice into a traditional clay or terracotta mug for a more rustic serve.
Always dry shake egg white first before adding ice - this builds a denser, more stable foam. Serving in a clay or terracotta mug is not merely aesthetic; the porous material subtly cools and aerates the drink, echoing the earthy mezcal character.
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