The Boulevardier, Negroni's evil twin

Like bourbon/rye-based cocktails? Gin's all the rage, so sure many have tried a decent Negroni, but what about a Boulevardier?

• 50 ml bourbon/rye whiskey (I prefer rye as it gives a slightly drier finish)
  
• 25 ml Campari
  
• 25 ml sweet Vermouth (worth experimenting with brands)
  
• dash orange bitters (optional)
  
• slice of orange (garnish; optional)
  
• ice
  

Add all but garnish and ice to large rocks glass and mix well. Add plenty of ice, swirl and enjoy. If you're feeling fancy, add orange slice garnish.