Sprinkle the brisket with salt and pepper and put it in a large slow cooker.
Evenly sprinkle one packet of Lipton Onion Soup over the brisket.
Cut the cranberry sauce into chunks and add to the ingredients in the slow cooker.
Cook on low for 8 hours. The brisket should be fork tender or falling apart.
Remove to a plate. When it is cool, wrap it tightly in foil and put it in the frig.
Put the liquid in a tight-fitting container in the fridge.
When you are ready to serve the beef brisket, slice it cold against the grain and arrange it in an oven-proof dish. Take the solidified excess fat off the juice and pour the liquid over the beef. Cover with foil.
Heat it in a 350° oven until hot and bubbly. Serve.