Best Beef Brisket

Ingredients

• 1 (4-5 lb.) beef brisket, flat cut preferred, trimmed
• kosher salt & freshly ground black pepper
• vegetable oil
• 2½ lbs. onions, halved and sliced ½ inch thick
• 1 Tbs. brown sugar
• 3 garlic cloves, minced
• 1 Tbs. tomato paste
• 1 Tbs. paprika
• ⅛ tsp. cayenne pepper
• 2 Tbs. all-purpose flour
• 1 cup low-sodium chicken broth
• 1 cup dry red wine
• 3 bay leaves
• 3 sprigs fresh thyme
• 2 tsp. cider vinegar