First, place a coupe or rocks glass in the freezer 15-30 minutes before making the cocktail. Next, clean the skin of a grapefruit. Then, use a y-peeler or cheese peeler to create a roughly 1in x 3in (2.5cm x 7.6cm) long strip of grapefruit peel. Clean up the edges, shaping the peel into a parallelogram with a knife. Then, create a slit down the center of the peel leaving roughly .5in (1.3cm) of clearance at the top and bottom. Set your garnish aside.
Next, cut and juice the grapefruit. Strain its contents into a separate container for the cocktail. Next, crack the egg and separate the yolk from the white. Whisk the egg white to loosen the protein structure up a bit and set it aside.
Now, measure out and add all the listed cocktail ingredients to a shaker. Cover and shake for 15 seconds without ice (dry shake). Then, top with ice, close the shaker, and vigorously shake everything for about 30 seconds.
Double strain the cocktail through a Hawthorne and fine mesh strainer, into either a coupe glass (sans ice) or a rocks glass (with a large ice cube). Express the grapefruit peel over the drink by holding the top and bottom of peel horizontally and facing out. Squeeze down to release the oils. Rub the outside of the peel against the rim of the glass. Twist the peel after it's expressed and slide it onto the rim of the glass using the slit in the center.