Tangy and melt-in-your-mouth tender, this is the BEST sweet and sour brisket! Perfect for your holiday table or any day of the week.
Preheat the oven to 400 degrees F. Season the brisket generously on both sides with kosher salt and pepper.
Heat the oil in a dutch oven over med/high heat (or a roasting pan if your brisket is too large to fit the dutch oven). Brown the brisket on both sides, about 3-4 mins per side and remove to a plate.
Add the sliced onion directly to the pan (tossing well) and cook until it begins to soften and brown, about 4 mins.
Add the garlic, dark brown sugar, and cider vinegar. Season with kosher salt and pepper and cook until the onions are very soft and beginning to caramelize, about 5 mins more.
Stir in the tomato paste, mustard, soy sauce, and tomato sauce. Stir well.
Add the 2 cups of the beef stock, stir, and return the brisket and any accumulated juices back to the pan. Season with salt and pepper. Use a large spoon ot tongs to cover the brisket well with the onions and sauce. The brisket should be partially submerged.
Cover tightly and place the dutch oven into the oven. Reduce the heat to 350 and cook for 1 1/2 hours.
Uncover, add the remaining 1/2 cup stock to the pan, and nestle the potatoes and carrots under and around the brisket. Spoon more sauce over the top of the meat. Cover and continue to cook one more hour.
Remove the brisket from the oven, uncover, and flip the brisket over. Stir the potatoes and carrots around and spoon some sauce over the top of the meat.
Return to the oven, uncovered, and continue to cook until brisket is very tender, about one more hour (it should flake easily when prodded with a fork). Add more stock if the sauce becomes too thick or begins to dry out.
Remove from the oven and use tongs to place the brisket on a cutting board, fat-side up. Cover with foil and let it rest for 15 mins.
Place the dutch oven on the stove over med/low heat. Spoon any excess fat off of the surface. Taste and adjust the seasoning. Stir in 1 Tbsp minced parsely.
After the meat has rested, slice the brisket into thin slices against the grain.
Serve with the potatoes and carrots on the side and the sauce spooned over the top. Sprinkle with minced parsley.