Preheat the oven to 375 degrees F (190 degrees C).
Place the brisket in a roasting pan fat side up. In a medium bowl, stir together the ketchup, soup mix and ginger ale; pour over the brisket. Arrange carrots and onion around the edge of the roast if using. Cover the roast with a lid or aluminum foil.
Bake for 2 hours in the preheated oven. Remove the cover, and cook for 1 more hour. Let stand for a few minutes before slicing and serving.