Chill a coupe or Nick & Nora glass by filling it with ice and cold water while you prepare the cocktail, or place it in the freezer for a few minutes.

Dry shake (if using egg white)

In a cocktail shaker, combine the rye, lemon juice, lime juice, simple syrup, Contratto Fernet, chocolate mole bitters, and egg white. Seal the shaker and dry shake (no ice) vigorously for 15–20 seconds to emulsify and build a silky foam.

Wet shake

Add a handful of ice to the shaker (enough to chill well). Shake vigorously for 12–15 seconds until the shaker is frosty and well chilled.

Strain

Discard the ice and water from the chilled glass. Double-strain the cocktail into the chilled coupe or Nick & Nora glass using a Hawthorne strainer and fine mesh strainer to catch any small ice shards and egg white solids, yielding a smooth, silky drink.

Garnish & Finish

Express the oils of a citrus twist over the surface of the cocktail, then either drop the twist into the drink or rest a dehydrated orange wheel on the rim. Lightly grate a little dark chocolate or dust with cocoa powder over the foam for an aromatic mole note (optional).

Serve

Serve immediately. The cocktail yields a balanced interplay of spicy rye, herbal fernet, bright citrus, and chocolate-mole bitters with a smooth foamy texture if egg white is used.