White BBQ Brisket Sandwiches

• 3 pounds beef brisket
• 1 large spanish onion thinly sliced
• 5 cloves of garlic minced
• 3 tablespoons olive oil
• 1 1/2 cups peeled tomatoes blended
• 1/2 cup Worcestershire sauce 
• 2 tablespoons apple cider vinegar
• 2 tablespoons Dijon mustard
• 1 tablespoon brown sugar
• 1/2 cup ketchup
• 1 tablespoon chili powder
• 1 canned chipotle pepper in adobo
• salt and pepper to taste

FOR THE BUTTERMILK BISCUITS:

• 4 cups all purpose flour plus more for dusting
• 1/2 tsp baking soda
• 2 tablespoons baking powder
• 2 teaspoons kosher salt
• 12 tablespoons VERY COLD unsalted butter cut into small cubes
• 2 cups buttermilk

FOR THE PIMENTO CHEESE:

• 1 3-ounce package cream cheese, room temperature
• 1 cup grated sharp cheddar
• 1 cup grated monterey jack
• 1/2 cup mayonnaise
• 1 tsp garlic powder
• 2 to 3 tablespoons Pimentos smashed
• 1 teaspoon grated onion
• salt and pepper to taste

FOR THE WHITE BBQ SAUCE:

• 3/4 cup mayonnaise
• 2 tablespoon water
• 2 tablespoon apple cider vinegar
• 1/2 tsp salt
• 2 tsp coarsely ground pepper
• 1 1/2 tsp mustard
• 1/2 tsp sugar
• 2 garlic clove minced
• 1 tsp prepared horseradish