Pre-heat oven to 350. Use a large roasting pan, ideally with a lid.
Stir together chili sauce, onion soup mix and beer in the bottom of the roasting pan.
Place brisket on top of the mixture along with the carrots.
Cover with lid and roast 2 - 2 ¼ hours.
Cool meat in pan (covered) until you can put the entire pan in the refrigerator overnight.
The next morning remove the thick layer of congealed fat that has solidified on the surface of the meat. (The fat gives the gravy and meat wonderful flavor in the roasting process but then most of it is no longer needed!)
Slice the cold brisket - against the grain - and place back in the gravy.
At this point it can be put back into the fridge until you are ready to finish the roasting with the potatoes.
When ready to roast add chunks of potatoes and the onions to the pot.
If using tomatoes, add now as well as cup of red wine.
Cover the pan and roast for another hour to an hour and a half.