Combine espresso, bourbon, simple syrup, and bitters in a shaker and fill with ice. Stir with a bar spoon for 30 seconds and strain into a rocks glass filled with ice. Twist lemon peel over the drink and rub around the rim of the glass. Garnish with lemon peel, optional.
There's a new Whiskey bar near the Elbow Room in Downtown Bismarck called Roundhouse and I'm sure they do craft cocktails. The bartender would actually be happy if you asked for this one.