Add the mezcal, lime juice, Cointreau, simple syrup and egg white to a cocktail shaker without ice. Shake for 15 seconds.
Add the ice to the cocktail shaker. Shake again for 30 seconds.
Strain the drink into a cocktail glass; the foam will collect at the top. Garnish with a dash of bitters on the foam, and use a toothpick or stir stick to gently draw a line to make a heart shape.