Step 1In a heavy-bottom 3- to 4-quart pot, combine the onion, garlic and bourbon. Bring the bourbon to a simmer over medium-high heat, then reduce the heat to maintain a gentle simmer and continue to cook until the onion is translucent, about 10 minutes.
Step 2Stir in the pepper, chile powder, dried mustard, salt, tomato paste, ketchup, cider vinegar, liquid smoke, Worcestershire sauce, dark brown sugar, Tabasco and maple syrup, if desired, for a sweeter sauce. Continue to gently simmer for 30 minutes to give the flavors time to marry. Stir frequently, making sure to scrape the bottom of the pot to prevent burning.
Step 3Remove from heat and purée the sauce until fairly smooth using an immersion blender or blending in stages using a stand blender. Set aside to cool, then refrigerate, covered, in a non-reactive container for up to 2 weeks. This sauce can also be frozen.