Add 2 oz bourbon (or rye) to a mixing glass
Add 1/4 to 1/2 oz simple syrup (adjust to taste)
Add 2 dashes bitters
Add 1 dash water (optional, to soften)
Stir with ice until well chilled (about 20–30 seconds)
Strain into a rocks glass over a large ice cube
Garnish with an orange peel (express oils over the drink, then discard)