Add the bourbon, cold brew concentrate, maple syrup, Angostura bitters, and chocolate bitters to a mixing glass.
Fill with ice and stir with a bar spoon for about 15-20 seconds, until the cocktail is well chilled and properly diluted.
Place one large ice cube or a few regular ice cubes in a rocks glass and strain the cocktail over the ice.
Hold the orange or lemon peel over the glass with the colored side facing the surface of the drink and gently bend it to express the oils.
Run the peel around the rim of the glass and add it to the cocktail
Serve immediately.
Notes
The cocktail should remain bourbon-forward. If your cold brew concentrate is especially strong, reduce it from ⅔ ounce to ½ ounce.For a sweeter drink, increase the maple syrup to about ⅓ ounce.Simple syrup can replace the maple syrup, although the flavor will be slightly more neutral.Use unsweetened, chilled cold brew concentrate for the best results.A large ice cube is ideal for serving because it melts slowly, but regular ice cubes work just fine.Orange peel gives the drink a classic bourbon-friendly citrus aroma. Use lemon peel if you'd prefer something brighter and slightly sharper.