In a cocktail shaker, combine the Scotch whisky, fresh lemon juice, simple syrup, egg white, and Angostura bitters.
Dry shake the ingredients (without ice) for about 15 seconds to help emulsify the egg white. Then add ice and shake for another 15 seconds until the mixture is well chilled.
Fine strain the cocktail into a chilled rocks glass over fresh ice. Express an orange twist over the drink to release its oils and garnish with the twist.