Equal parts:
Booker's (or other high-proof) bourbon - adust the bourbon up to balance.
Punt e Mes

Place a rocks glass in the freezer for about 15 minutes before making the cocktail.

Fill a mixing glass about halfway with ice. Add bourbon and Punt e Mes. Stir until drink is well chilled, about 20 seconds. Strain into chilled rocks glass. Serve.

Via http://www.seriouseats.com/recipes/2014/05/moto-guzzi-cocktail-h...

"This two-ingredient drink was created by Boston bartender John Gertsen. Gertsen and his fellow bartender Kevin Montuori were riffing on Manhattan variations, especially ones using high-proof Booker's bourbon. Punt e Mes is an Italian vermouth, more bitter than most sweet vermouths. At 120+ proof, Booker's can take Punt e Mes on head to head, so the Boston barkeeps decided 50-50 was the way to go. Because of Punt e Mes's bitterness, this drink doesn't call for the addition of bitters."