Add the granulated sugar and Angostura bitters to a rocks glass, then add the water. Muddle until the sugar is mostly dissolved into a paste, 20–30 seconds.
Pour in the bourbon and stir to dissolve any remaining sugar, 10–15 seconds.
Add a large ice cube and stir until the glass feels very cold and the drink is slightly diluted, 20–30 seconds.
Express the orange peel over the surface, rub the rim with the oils, then place the peel in the glass and serve immediately.