There's no better sign that fall has arrived than a basket of crisp apples on the kitchen counter. Whether you pluck them straight off the tree at an orchard or pick them up from a vender at the farmers' market, it's hard to resist eating them out of hand, but try to save a few for this recipe. The cinnamon and brown sugar echo the flavor of traditional apple, pie, but in this recipe you use only the skin of the apples, a tip I picked up from Bobby Heugel at Houston's Anvil Bar (the peel introduces bitterness and apple flavor without the added sugar and water that would make the solution too sweet). This bitters adds a sweet spiciness to bourbon, rye, whiskey, applejack, or apple brandy, and is also just dandy in an old-fashioned or Manhattan.
Place all of the ingredients except for the bourbon, water, and rich syrup in a quart-sized Mason jar or other large glass container with a lid. Pour in the two cups of bourbon, adding more if necessary so that all the ingredients are covered. Seal the jar and store at room temperature out of direct sunlight for 2 weeks, shaking the jar once a day.
After 2 weeks, strain the liquid through a cheesecloth-lined funnel into a clean quart-sized jar to remove the solids. Repeat until all of the sediment has been filtered out. Squeeze the cheesecloth over the jar to release any excess liquid and transfer the solids to a small saucepan. Cover the jar and set aside.
Cover the solids in the saucepan with the water and bring to a boil over medium-high heat. Cover the saucepan, lower the heat, and simmer for 10 minutes.
Remove the saucepan from the heat and let cool completely. Once cooled, add the contents of the saucepan (both liquid and solids) to another quart-sized Mason jar. Cover the jar and store at room temperature out of direct sunlight for 1 week, shaking the jar daily.
After 1 week, strain the jar with the liquid and solids through a cheesecloth-lined funnel into a clean quart-sized Mason jar. Repeat until all of the sediment has been filtered out. Discard the solids. Add this liquid to the jar containing the original bourbon solution.
Add the rich syrup (a simple syrup made with 2 cups Demerara or turbinado sugar to 1 cup of water) to the jar and stir to incoporate, then cover and shake to fully dissolve the syrup.
Allow the mixture to stand at room temperature for 3 days. At the end of the 3 days, skim off any debris that floats to the surface and pour the mixture through a cheese-cloth lined funnel one last time to remove any solids.
Using a funnel, decant the bitters into smaller jars and label. If there's any sediment left in the bottles, or if the liquid is cloudy, give the bottles a shake before using. The bitters will last indefinitely, but for optimum flavor use within a year.