Preheat your oven to 300 degrees Fahrenheit (150 degrees Celsius).

In a generously-sized (15-inch) oven-proof skillet, set over medium-high heat, add both the oil and butter.

Season the chicken thighs with a sprinkling of salt and a dash of black pepper. Gently lay these seasoned chicken thighs in the skillet, allowing them to sear and develop a golden brown hue, which should take about 5 minutes per side. Once browned, remove the chicken from the skillet, keeping it warm.

If desired, you can spoon off any excess grease from the skillet.

Next, add the diced onion to the skillet and cook until it turns soft and translucent, typically around 4 minutes.

Now, pour the whisky into the skillet with care and continue to cook the onions for an additional 5 minutes, allowing the whisky to gently reduce and infuse its flavors into the onions.

To this flavorful mixture in the skillet, add the barbecue sauce, and if your barbecue sauce is notably thick, a touch of water. Incorporate the peach preserves and Worcestershire sauce, stirring thoroughly to blend all the components.

Nestle the seared chicken back into the sauce, ensuring it's evenly coated. Scatter the peach slices around the chicken in the skillet.

Cover the skillet securely with aluminum foil and transfer it to your preheated oven. Let it bake for approximately 90 minutes or until the chicken reaches a delightful level of tenderness where it practically falls off the bone.