Classic Barbecue Sauce

From The Art of Real Food, Seasonal Recipes for Every Week of the Year, by Joanne Neft and Laura Kenny:

2 tablespoons grapeseed oil
1 medium onion, finely chopped
3 or 4 large ripe tomatoes, finely diced (skin removed)
1/2 cup red wine vinegar
1/2 cup brown sugar, packed
2 tablespoons Worcestershire sauce
1/2 teaspoon salt
1/2 teaspoon pepper
Heat oil in a 3-quart pan over medium heat. Add onions; cook, stirring often, until soft, about 10 minutes.

Stir in tomatoes, vinegar, brown sugar, Worcestershire sauce, salt and pepper. Bring to a boil, reduce heat and simmer, uncovered, until thickened, about 1 hour. Stir occasionally to prevent sticking. When cool, cover and refrigerate. Keeps in refrigerator up to 2 weeks.