Prep Glass: Fill an Old Fashioned or Rocks glass with ice and give it a quick stir. Set it aside.
Add Egg White (optional): Crack open an egg, separate white from yolk and pour the white into the shaker. Discard the yolk.
Add Simple Syrup: Add ¾ oz simple syrup.
Add Yuzu Juice: Measure and pour ¾ oz Yuzu juice into the shaker.
Add Whisky: Pour 2 oz Japanese Whisky of your choice into the shaker.
Shake Well: Fill the shaker with ice. Close it well and shake the ingredients vigorously for about 15 seconds.
Dry shake (only if using egg white): Open the shaker. Using the cocktail strainer, pour the liquid into the other tin and discard the ice. Close the shaker again and shake another time, for 15-20 seconds, without ice this time. If you’re not using egg white, you can skip this step.
Strain: Discard the ice in the Old Fashioned glass and refill it with fresh, new ice cubes. Use the cocktail strainer to pour the drink into the ice-filled glass.
Garnish: Garnish with a lemon slice or a lemon zest. To do so, express the lemon peel on top of the glass; you can either discard it afterward or place it on the rim of the glass for an added citrus touch. Serve immediately.