Place a large ice cube, or a couple regular ice cubes, in a whiskey glass (or small water glass or Tigger mug).
Pour the bourbon over the ice cube. Add the simple syrup and ginger bitters. Stir for 30 seconds, until cold and properly diluted. Note: I add the simple syrup after the bourbon, so the simple syrup doesn't settle at the bottom of the glass.
Twist the orange and/or lemon peel over the old fashioned. Tuck it into the side of the ice cube. Enjoy!
*If you're using sugar cubes: Use the handle of a wooden spoon to muddle the sugar cube with the ginger bitters. Add the ice and bourbon. Stir until cold and properly diluted, about 30 seconds. Finish with a twist. Enjoy!