Preheat oven to 350 degrees
Place the flour in the oven bag, and shake
Place chuck roast in bag, place the bag into a 13x9-inch baking pan, and add the potatoes, carrots, celery and onions around the roast
Place the garlic cloves on the roast, and sprinkle with dry soup mix
Pour the beef broth in the bag, and use the ties to close up the bag
Using a sharp knife, cut 6 slits in the top of the bag to allow steam to escape
Place roast in oven, and bake for 1 ½ to 2 hours or until roast and vegetables are tender, and internal temperature of roast is over 160 degrees according to a meat thermometer
Optional, remove roast and vegetables from bag, shred or cut roast into large pieces, place into baking dish, with cooking liquids, cover, and bake at 325, adding more broth if needed, until ready to eat