Place the whiskey, lemon juice and pumpkin spice syrup in a cocktail shaker and shake a minute to combine.
Add a cube of ice and the egg white and shake a couple minutes until well combined, chilled and the top is frothy. Strain into a rocks glass, either as it is or over an ice cube.
Notes
1 egg white is around 2 tablespoon (30ml). You can use a full egg white if you like or just half - the more you use, the more of a foamy top layer you are likely to get.