Add bourbon, gin, honey syrup, ginger liqueur, bitters, and egg to the shaker. Dry shake for 10–12 seconds (no ice).
Add cubed ice. Shake again until well chilled.
Strain into a chilled glass. Grate fresh nutmeg over the top. Serve immediately.
Notes
Fresh eggs give the best texture. Use whole egg for richness, or egg white for a lighter drink. Try maple syrup for a twist. Small glass is best. Letting the drink warm slightly brings out the spices.