- 1 tablespoon unsalted butter
- 1 tablespoon vegetable oil
- 1 1/2 cups chopped onion
- 4 garlic cloves, minced
- 1 serrano chile, minced
- 1 cup ketchup
- 1 cup brewed espresso
- 1/4 cup distilled white vinegar
- 3 tablespoons unsulfured molasses
- 2 teaspoons chile powder
- 1 teaspoon kosher salt
- 1 teaspoon sugar
- 1/4 teaspoon Worcestershire sauce
- In a large saucepan, melt the butter in the oil. Add the onion, garlic and serrano and cook over moderately low heat, stirring occasionally, until the onion is softened, about 8 minutes. Stir in all of the remaining ingredients and bring to a simmer. Cover and cook the sauce over low heat for 30 minutes, stirring occasionally.
- Scrape the sauce into a food processor and puree until smooth. Transfer to a bowl and let cool, then cover and refrigerate overnight to allow the sauce to mellow.
The barbecue sauce can be refrigerated for up to 2 weeks.