In a chilled rocks glass, combine bitters, maple syrup and spirits.
Stir gently with a large rock of ice for several turns
Garnish with an orange twist
I generally prefer using an overproofed whiskey when making old fashioned variations, and this is no exception. I had good results with Old Forester 1920.
I'm typically not a big fan of putting good scotch in cocktails, but something like the Laphroaig 10, or Ardbeg 10 works nicely. In a pinch, or when pinching pennies, I've used the Shieldaig Islay expression, which isn't great on its own, but imparts the desired base flavor profile.
This drink is meant to be built in the glass, and waters down well. The flavor profile shifts as the ice melts, and I find it relatively enjoyable throughout.
Using marginally less maple syrup might be desirable depending on how sweet you prefer the drink, but real maple syrup is key to bringing the rest of the flavors together.