Make the BBQ Sauce. Heat the oil in a medium pot over medium heat. Add the chopped onion and garlic and saute, stirring frequently, until the onions are translucent and slightly golden brown, about 5 minutes. Add the bourbon, and simmer for 2-3 minutes. Stir in the tomato paste, and cook for an additional 2-3 minutes or until the paste darkens slightly. Add the prune purée, Worcestershire sauce, soy sauce, maple syrup, apple cider vinegar, Dijon mustard, paprika, salt and pepper. Whisk to combine.
Bring to a simmer, reduce heat and cook for 30 minutes to incorporate the flavors. Stir in the liquid smoke, if using. Taste for seasoning and add additional salt and pepper if desired.
Make the pulled chicken. Put the chicken thighs into the stainless inner cooking pot of an Instant Pot. Pour 1 cup of the BBQ sauce and chicken broth over the chicken and toss to coat. Sprinkle the mixture with the garlic powder, onion powder, salt and pepper and stir again to combine.
Place the lid on the Instant Pot making sure the valve is in the sealed position. Press manual (high pressure) and set to 12 minutes. When it’s done, carefully turn the valve to release the steam (quick release style). Use a clean dishcloth to mute the sound and the steam that billows out. Remove the lid and using a slotted spoon, scoop the chicken out of the instant pot into a serving bowl. Shred chicken with two forks and stir in reserved BBQ sauce.
Serve chicken on buns topped with coleslaw.