In a mixing glass, stir together Irish whiskey and simple syrup.
Add a large ice cube to a rocks glass, and pour the whiskey over the top.
Add a few dashes of orange bitters, and garnish with a piece of orange zest.
Notes
Make a batch of large ice cubes or ice spheres the day before (or keep a stash in your freezer). The large surface area means it melts more slowly than a bunch of tiny ice cubes.Use a vegetable peeler to peel a thin layer of peel off a fresh orange, being careful to avoid the white pith.Before adding it to your drink, gently twist the orange peel and rub it around the edge of the glass before dropping it in to release more of the oils into your drink.Angostura bitters can be used in place of orange bitters.