Rinse the huckleberries under cold water and remove any stems or debris.
Heat the oil in a saucepan over medium heat. Add the onion and cook until softened, about 5 minutes.
Stir in the salt, chili powder, Worcestershire sauce, smoked paprika, dry mustard, pepper, chili flakes, and cumin. Cook for another minute until fragrant.
Add the tomatoes, vinegar, brown sugar, and molasses. Bring to a simmer, then reduce heat and cook, covered, for 1 hour.
Add the huckleberries and simmer gently, uncovered, for an additional 25 minutes, or until the berries are softened.
For a smoother sauce, transfer the mixture to a blender and puree until mostly smooth. Leave some chunks for texture if you prefer.
Stir in the butter for extra richness, if desired. (optional)
Season with additional salt or pepper to taste.
Let the sauce cool slightly, then transfer it to sterilized jars. Store in the refrigerator for up to 2 weeks or freeze for up to 3 months.