In a mixing bowl, combine beef gravy, Italian salad dressing, Lipton Onion Soup Mix, mushrooms, and black pepper.

Place the beef brisket in a shallow roasting pan.

Pour the gravy mixture evenly over the brisket.

Cover the roasting pan tightly with aluminum foil to seal in moisture.

Bake in a preheated oven at 300°F (150°C) for 4 hours. Ensure the foil remains sealed during baking.

After 4 hours, remove the roasting pan from the oven.

Allow the brisket to rest in the pan, still covered with foil, for 10-20 minutes to allow the juices to redistribute.

Carefully remove the brisket from the pan and place it on a cutting board.

Slice the brisket thinly across the grain to ensure maximum tenderness.

Serve immediately, spooning the remaining gravy over the sliced brisket.