If using an egg white, separate a fresh egg and measure roughly half an egg white (about 0.5 egg). Chill a coupe or rocks glass by filling with ice or placing in the freezer briefly.

Add rye whiskey (2 oz), peach liqueur (0.5 oz), fresh lemon juice (0.75 oz), fresh grapefruit juice (0.5 oz), simple syrup (0.5 oz), Angostura bitters (2 dashes) and the egg white (0.5 egg) into a cocktail shaker.

Dry shake (no ice) vigorously for 15–20 seconds to emulsify the egg white and build a dense foam. This step is optional if you omitted the egg white.

Add about 1 cup of ice to the shaker and shake again vigorously for 10–15 seconds until the shaker is very cold to the touch and properly diluted (you should see condensation).

Double strain the cocktail into the chilled coupe or a rocks glass over fresh ice (if you prefer it on the rocks) using a fine-mesh strainer in addition to the shaker strainer to ensure a silky texture without ice shards.

Express the oils of the grapefruit twist over the drink by holding the twist skin-side down above the glass and pinching it to release the oils, then drop the twist into the glass as garnish.

Finish with a light pinch of cracked black pepper on the foam or rim for an aromatic, slightly savory note (optional).

Serve immediately.