Preheat the oven to 300 degrees F.

Place the brisket in a pan, fat side up. Slice the onion and place the rings along with the carrots around the meat.

Sprinkle the onion soup mix on top of the meat, pressing to adhere. Sprinkle the brown sugar over the meat.

Bake uncovered for 30 minutes to "set."

Remove brisket from oven and distribute the cranberries over the meat.

Cover the pan tightly and continue to cook at 300 degrees F for three hours. By now a nice gravy has formed around the meat/veggie combination. Baste the brisket to add moisture to the top. Cover and cook an additional hour (or until fork-tender.)

Cool and slice thinly. Add slices to gravy in pan, cover and gently reheat.