1 (5 pound) bone-in beef pot roast
salt and pepper to taste
1 tablespoon all-purpose flour, or as needed
2 tablespoons vegetable oil
8 ounces sliced mushrooms
1 medium onion, chopped
2 cloves garlic, minced
1 tablespoon butter
1 1/2 tablespoons all-purpose flour
1 tablespoon tomato paste
2 1/2 cups chicken broth
3 medium carrots, cut into chunks
2 stalks celery, cut into chunks
1 sprig fresh rosemary
2 sprigs fresh thyme