Add 2 oz bourbon to a mixing glass
Add 1/4 oz simple syrup (or 1/4 oz sugar syrup)
Add 2 dashes Angostura bitters
Add 1 dash orange bitters (optional)
Stir with ice for 20–30 seconds
Strain into a rocks glass filled with a large ice cube
Garnish with an orange peel
Express orange peel oils over the top, then place peel in the glass