How to Make It
Heat oil in a heavy medium saucepan over medium heat. Add onion and cook, stirring often, until softened, about 10 minutes. Stir in garlic and cook 1 minute more.
Stir in vinegar, Worcestershire sauce, chili powder, and plum tomatoes and let simmer and thicken 5 minutes, breaking up tomatoes with a wooden spoon or spatula.
Remove from heat. Stir in salt, pepper, horseradish, and Tabasco, then blend until smooth with an immersion blender (or use a stand blender). Serve with smoked brisket.
B-Side BBQ, Oakland