1. Preheat oven to 325°.
2. Combine first 3 ingredients in a small bowl; stir in 1 teaspoon salt. Rub spice mixture evenly over both sides of brisket. Heat a Dutch oven over medium-high heat. Add oil to pan; swirl to coat. Add brisket; sauté 3 minutes on each side or until browned. Remove brisket from pan. Add beer; bring to a boil, scraping pan to loosen browned bits. Add broth and garlic; return to a boil. Return brisket to pan. Cover and cook at 325° for 2 hours. Turn brisket over; cook an additional 2 hours. Turn brisket over. Add carrot, celery, and onion; cook an additional 1 hour or until brisket is very tender.
3. Remove brisket and vegetables from pan using a slotted spoon. Skim fat from cooking liquid; discard fat. Bring cooking liquid to a boil over medium-high heat. Place flour in a small bowl; stir in 1/2 cup water. Add flour mixture to pan, stirring until smooth; bring to a boil, stirring constantly. Cook 2 minutes or until slightly thickened. Stir in remaining 1/4 teaspoon salt. Serve the sauce with beef and vegetables.