Tomato Onion Brisket

1 2nd cut brisket; 1 jar marinara sauce; 2 large onions. Slice onions and lay in bottom of a parchment lined 9×13 pan, or baking dish. Place brisket on top and cover with marinara. Seal with with foil and bake on 275 for 4 – 5 hours. Cool and slice. You can freeze at this point, or return to oven for another hour at 275 to soften the meat even more. Be sure all pieces are covered in the sauce before reheating.