Add coffee-infused bourbon, brown sugar syrup, and bitters to a mixing glass. Add ice. Stir until chilled, about 20 seconds. Strain into a double rocks glass over one large ice cube. Take the sliver of orange peel between your thumb and index fingers and pinch to express the citrus oils into the glass, run around the rim and drop into the glass.
Coffee-Infused Bourbon
In a mason jar, add 3 tbsp whole coffee beans (I used dark roast) to 1 cup of bourbon. Close and shake well. Let sit at room temperature for 8-12 hours. Taste every four hours to check the flavour. Strain off coffee beans and keep in the fridge. Infused bourbon will keep for quite a while.
Brown Sugar Syrup
Combine brown sugar and water in a small saucepan over medium heat, bring to a simmer, stirring often, until sugar is dissolves. Remove from heat and bring to room temperature before using. Syrup will keep in an airtight container in the fridge for at least 2 weeks.