Combine 1/2 cup water and 1/2 cup sugar in a small saucepan over medium heat. Add 2 whole cinnamon sticks. Stir until sugar dissolves, bring to a gentle simmer for 3 minutes, then remove from heat and let cool with the sticks for at least 20 minutes. Remove cinnamon sticks and bottle. Store refrigerated up to 2 weeks.

Chill a coupe or cocktail glass in the freezer or fill it with ice water to cool while you build the drink.

In a cocktail shaker, add the gin, fresh lemon juice, chilled grapefruit juice, cinnamon syrup, dry Curaçao and egg white (if using).

Dry shake (no ice) vigorously for 15–20 seconds to emulsify the egg white and produce a silky foam. If not using egg white, skip the dry shake.

Add a generous handful of ice to the shaker (about 4–6 large cubes) and shake hard for 12–15 seconds until the shaker is very cold to the touch and slightly frosted.

Double-strain the cocktail into the chilled coupe or cocktail glass using a Hawthorne strainer and a fine mesh strainer to remove ice shards and create a smooth texture.

Add 2 dashes of Angostura bitters on top of the foam (if present). Use a toothpick to drag a small line or a decorative pattern through the bitters if desired.

Garnish & Finish

Express the oils of a grapefruit twist over the drink by holding the twist skin-side down above the glass and giving it a quick squeeze, then run the peel around the rim and drop it into the drink or rest it on the rim.

Optionally dust a very light pinch of ground cinnamon over the foam for aroma and visual appeal.

Serve immediately. This recipe makes one cocktail.