Combine the beef consomme, soy sauce, lemon juice, liquid smoke and garlic in a large roasting pan (a disposable is just fine). Place the brisket in the marinade, fat-side up. Cover tightly with foil. Marinate in the refrigerator for 24 to 48 hours.
When ready to cook, preheat the oven to 300 degrees F.
Cook the brisket in the foil-covered pan until fork-tender, about 40 minutes per pound (6 to 7 hours). Transfer to a cutting board, slice against the grain and put the slices back into the cooking liquid. Serve immediately, spooning the juice over the slices. (Barbecue sauce may be used, if preferred.)
You may store the pan in the fridge for up to 2 days, or freeze for use at a later date. If fat collects and hardens at the top, remove and discard.
Brisket is great with mashed potatoes, with the juice spooned over the top. It is also great on a sandwich with melted cheese.