Barbecue Brisket Sandwich with Herb Sour Cream

Serves:

• FOR BRISKET:
• 1 onion, finely chopped
• 1/4 cup smoked paprika
• 1 tablespoon chili powder
• 1 tablespoon chopped fresh oregano
• 1 tablespoon fresh thyme leaves
• 1 tablespoon sugar
• 1 tablespoon freshly ground black pepper
• 3 garlic cloves, finely chopped
• 1 (4-pound) piece beef brisket (well marbled and with top layer of fat intact)
• 1 stalk celery, cut into 3 pieces
• 1 large carrot, cut into 3 pieces
• 2 cups beef stock
• FOR BBQ SAUCE:
• 2 tablespoons unsalted butter
• 2 medium onions, chopped
• 1 small celery stalk, finely chopped
• 2 cups beef stock
• 2 cups ketchup
• 1 cup white distilled vinegar
• 3 cup (packed) light brown sugar
• 1/4 cup fresh lemon juice
• 3 tablespoons Worcestershire sauce
• 2 tablespoons steak sauce
• 1 1/2 teaspoons chili powder
• 1 teaspoon hot sauce
• 1 teaspoon paprika
• 1 teaspoon salt
• 1/2 teaspoon dry mustard
• 1/2 teaspoon freshly ground black pepper
• SOUR CREAM SAUCE:
• 1 cup sour cream
• 1/4 cup chopped fresh basil
• 2 tablespoons chopped fresh flat leaf parsley
• 1 tablespoon chopped fresh dill
• 1 tablespoon chopped fresh tarragon
• SANDWICHES:
• 6 crusty rolls, halved horizontally, warm