Beef Brisket with sweet tomato sauce

A friend gave me this recipe a long time ago, it was her mother's.  I like it for something different to what I normally do and have been making it for years.  I have thought of cutting the sauce recipe in half, it makes quite a bit.  I never have, I love it too much with mashed potatoes.  It's a great no fuss recipe.  I hope you enjoy it.

3 pounds yellow onions, chopped
3 tablespoons light olive oil
5~6 pound brisket, trimmed
kosher salt
freshly ground black pepper
1 cup ketchup
6 tablespoons lemon juice, about 2 large lemons
2 tablespoons dark brown sugar, packed
2 cups canned tomato puree

In a large saute pan, saute the onions in the olive oil until they are golden brown.

Season all sides of the brisket with salt and pepper.  Over high heat brown the brisket well on all sides in its own fat in a large, heavy~bottomed pot.  Add the onions.  Transfer to a 325 degree oven for 4 hours, until fork tender.

Skim the fat from the juices and discard.  In a separate bowl mix together the ketchup, lemon juice, brown sugar, and tomato puree.   Add tomato mixture to the pan and cook another 30 minutes.  Remove the brisket from the pot, slice thinly across the grain, and return the meat to the sauce to keep warm.

I always serve extra sauce on the side with some mashed potatoes.