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