Stir together first 6 ingredients in a small bowl to form a paste. Rub on brisket, and let stand at room temperature 1 hour.
Preheat oven to 250°. Cook onion in hot oil in a large Dutch oven over medium-high heat, stirring occasionally, 5 minutes or until tender. Add 6 garlic cloves, and sauté 30 seconds. Remove from heat, and add beef broth, stirring to loosen browned bits from bottom of skillet. Place brisket in Dutch oven, fat side up. Spoon onion mixture over brisket.
Bake, covered, at 250° for 4 to 5 hours or until fork-tender. Let stand 30 minutes. Thinly slice brisket across the grain. Serve with Horseradish Cream.