A great all-around barbecue sauce from The Cook’s Illustrated Guide to Grilling and Barbecue. It tastes like it took all day to make, but it is really quite simple.
1 medium onion, peeled and quartered
1/4 cup water
1 cup ketchup
5 tablespoons molasses
2 tablespoons cider vinegar
2 tablespoons Worcestershire Sauce
2 tablespoons Dijon mustard
1 teaspoon hot pepper sauce, such as Tabasco
1/4 teaspoon ground black peppers
2 tablespoons vegetable oil
1 medium garlic clove, minced or pressed through a garlic press
1 teaspoon chili powder
1/4 teaspoon cayenne
Process the onion with the water in a food processor until pureed and the mixture resembles slush, about 30 seconds. Strain the mixture through a fine-mesh strainer into a liquid measuring cup, pressing on the solids with a rubber spatula to obtain 1/2 cup juice. Discard the solids.
Whisk the onion juice, ketchup, molasses, vinegar, Worcestershire, mustard, hot pepper sauce and black pepper together in a bowl.
Heat the oil in a large nonreactive saucepan over medium heat until shimmering but not smoking. Add the garlic, chili powder and cayenne. Cook until fragrant, about 30 seconds. Whisk in the ketchup mixture and bring to a boil. Reduce the heat to medium low and simmer gently, uncovered, until the flavors meld and the sauce has thickened, about 25 minutes. Cool the sauce to room temperature before using. The sauce can be refrigerated for up to a week.