Heat the oil in the cooker over medium high heat.
Season the brisket with salt and pepper. Sear the brisket on all sides until brown.
Remove the brisket and add the onion, carrots, celery, garlic, and bay leaves to the pot.
Spread the mustard all over the brisket. Sprinkle 1 envelope of soup mix on each side. Place the brisket, fat-side up, on top of the vegetables in the cooker, top the meat with the remaining vegetables. Pour the wine, Worcestershire over the meat and vegetables.
Close and lock the pressure cooker. Cook for 45 minutes on HIGH pressure.
Once the cooking time is done, without releasing pressure, remove the cooker from the burner. Use the natural release method to allow the pressure to come down, this may take several minutes.
Once the pressure inside has fully released, open the lid, remove the brisket from the pan and let it cool to room temperature.
Slice the meat against the grain, as thinly as possible. De-fat the sauce and place the sliced meat, sauce, and vegetables into a rectangular baking dish.
Sprinkle with the parsley and cover the dish with aluminum foil. Heat the brisket in a 325°F oven until hot. Serve with your choice of sides.