In a medium saucepan, heat the olive oil over medium heat. Add the finely diced onion and cook for 3–4 minutes until softened and translucent.
Stir in the minced garlic and unsalted butter. Saute for another 1–2 minutes until fragrant.
Pour in the apple cider vinegar and brandy or bourbon (if using). Let it simmer for 2–3 minutes to cook off some of the alcohol.
Stir in the apple butter, Worcestershire sauce, ketchup, brown sugar, salt, black pepper, and liquid smoke (if using).
Bring the mixture to a gentle simmer. Reduce the heat to low and let it cook uncovered for 15–20 minutes, stirring occasionally until thickened and well blended
For an ultra-smooth texture, blend the sauce using an immersion blender or transfer it to a standard blender (let cool slightly first).