Add two sugar cubes, or more if you like it sweet, to serving glass. Add 2-4 drops of bitters.
Add a slice of orange and muddle everything together until the sugar cube has dissolved.
Add bourbon/whiskey/rye. Rub orange peel around rim of serving glass to get orange oils and fragrance to release. Drop in orange peel and stir contents of drink together.
Add ice. Stir until chilled. Enjoy.