Cooking bags are a convenient way to effortlessly bake a dish while keeping the food from drying out. Pot roast can easily become too dry if you overcook it, but a cooking bag will help to decrease the chance that will happen. The bag keeps the moisture close to the food, allowing your pot roast to remain succulent. Another benefit to using cooking bag is that there are no dishes to clean since the food never touches the inside of the baking dish.
Preheat the oven to 325 degrees F. and put 1 tbsp. flour into the cooking bag. Shake the bag to coat the inside with flour.
Pour the 1/4 c. flour and the French onion soup into the bag. Hold the top of the bag closed with one hand and shake the bag to combine the flour and soup. You can also combine them in a separate bowl and pour them into the bag.
Place the pot roast, carrots, potatoes, celery and onions inside the cooking bag with the mixed soup and flour.
Holding the opening of the bag closed, turn the bag to cover the roast and vegetables with the soup mixture.
Close the bag with the tie that came with the bag. Make several 1/2" slits in the top of the bag to allow excess steam to escape.
Place the cooking bag in the oven and bake at 325 for two to three hours or until a meat thermometer placed into the deepest part of the meat reads 160 degrees. The roast should be tender and cut easily. Serve pot roast warm with the roasted vegetables.