To make Strong Chai Syrup, brew 2 parts tea with 1 part water over medium high heat. Let steep longer than usual. Remove tea bags and add 1 part sugar. Stir over heat until dissolved, then let cool.
Combine whiskey, lemon juice, chai syrup, and vanilla extract in a cocktail shaker without ice.
Dry shake vigorously to froth the egg white. Add ice then shake again until cold.
Strain into a coupe glass and garnish with a lemon slice (optional).
