This is one of my best recipes. It creates a very juicy and tender brisket and is very easy to make. The best brisket to use will have a little fat on it.
To make the marinade, whisk together the liquid smoke, steak sauce, salt, pepper, and garlic powder in a bowl.
Line a roasting pan with aluminum foil. Place brisket with the fattier-side facing upwards in the center of the pan. Pour half of the marinade over the brisket. Using a food injector, inject the rest of the marinade into the brisket. Seal the brisket in the foil and refrigerate for at least 16 hours.
Preheat oven to 250 degrees F (120 degrees C). Open foil and layer onion slices on the brisket. Reseal the foil.
Bake in preheated oven for 6 hours. Remove the brisket and slice. Reseal the foil and bake the sliced brisket for 1 hour more.
Per Serving: 882 calories; protein 39.2g; carbohydrates 10.6g; fat 75.4g; cholesterol 163.5mg; sodium 1986.2mg.