cut fat off brisket carefully. line 9x13 pan with foil, place brisket in pan. mix soup mix with 1 cup water and pour over brisket. add carrots and celery. cover brisket (like wrapping present). cook in 325 oven for 2 1/2 to 5 hours, depending on the size of the brisket. start checking after 2 1/2 hours. open pouch carefully as steam can burn. fork should pass through easily. can cook up to 5 hours.