Paraphrasing the Alembic bar in SF: The Old Fashioned is among the most clean and elegant cocktails, especially without the muddled fruit cocktail with which the old warhorse is so often saddled down with.
Add simple syrup and bitters to an old fashioned glass and twirl until bitters and syrup are completely mixed.
Fill glass with ice 3/4 of the way up and fill bourbon to just below that level (comes out to 2-2.5 ounces.)
Stir (do not shake!) Taste and then taste again 5 min later and the melt from the ice will create a dangerously drinkable bourbon cocktail.
Blood Orange Simple Syrup
Cut blood orange into very thin vertical slices (like medallions or rounds, not wedges) and set aside.
Mix sugar and water in a small sauce pan and heat over medium to medium to low heat until sugar is dissolved. Once dissolved add blood orange slices and cook 15-20 min until orange slices look limp.
Immediately jar and cool. Best to make ahead and have batch ready for cocktail hour. (Note: any 2:1 sugar syrup will work for the old fashioned. 1:1 doesn't pack enough punch while 2:1 takes off the bite of the bourbon with out making the cocktail too sweet.)