Preheat the oven to 325°F with a rack in the center position.
Pat the brisket dry and season all over with salt and pepper.
Heat the oil in a large Dutch oven or braiser over medium-high heat. Once the oil is glistening, add the brisket and cook, undisturbed, until browned, about 6 minutes per side.Transfer the meat to a plate and discard all but 2 to 3 tablespoons of fat.
Reduce the heat to medium low. Add the garlic, mustard, and tomato paste. Cook for 1 minute, or until the garlic is fragrant. Add the stock, vinegar and crushed tomatoes, scraping up any browned bits from the bottom of the pot.
Return the brisket (and any collected juices) to the pot, fattier side up. In a small bowl, mix together the thyme, oregano, garlic powder, paprika, and brown sugar. Sprinkle the seasoning over the brisket.
Add the onions to the pot. Increase the heat to medium and bring the liquid to a simmer. Cover the pot and transfer it to the oven. Cook for 2 hours. Remove the pot from the oven and add the carrots and potatoes, nestling them into the liquid. Cover the pot and return it to the oven for another 2 hours, or until the vegetables are tender and the internal temperature of the meat reaches 200°F on an instant read thermometer.
Transfer the brisket to a carving board and tent with foil to keep warm. Using a slotted spoon, transfer the vegetables to a serving platter.
Return the pot over medium heat and simmer the sauce, stirring, until slightly reduced, 3-5 minutes. Season to taste with salt and pepper.
Carve the brisket, cutting against the grain, into ½-inch thick slices and arrange on the serving platter with the vegetables. Pour the sauce over everything and serve.
Slow Cooker Method
Pat the brisket dry and season all over with the salt and pepper.
Heat the oil in a large Dutch oven or braiser over medium heat. Once the oil is glistening, add the brisket and cook, undisturbed, until browned, about 6 minutes per side. Transfer the meat to a 6-7 quart slow cooker.
To the same Dutch oven, add the garlic, mustard, and tomato paste. Cook for 1 minute, or until the garlic is fragrant. Add the stock, vinegar and crushed tomatoes, scraping up any browned bits from the bottom of the pot. Pour the liquid over the brisket in the slow cooker.
In a small bowl, mix together the thyme, oregano, garlic powder, paprika, and brown sugar. Sprinkle the seasoning over the brisket..
Add the onions to the slow cooker. Cook on HIGH for 5 hours. Add the potatoes and carrots to the slow cooker and cook on HIGH for another 2 hours.
Transfer the brisket to a carving board, carve the brisket, cutting against the grain, into ½-inch thick slices. Arrange on the serving platter with the vegetables. Pour the sauce over everything and serve.
Note: If you want to reduce the sauce a little, transfer it to a small saucepan set over medium heat and simmer, stirring, until slightly thickened.
Instant Pot Method
Pat the brisket dry and season all over with the salt and pepper.
Set the Instant pot to Sauté mode. Add the oil. Once the oil is glistening, add the brisket and cook, undisturbed, until browned, about about 6 minutes per side. Transfer the meat to a plate and discard all but 2 to 3 tablespoons of fat.
Add the garlic, mustard, and tomato paste. Cook for 1 minute, or until the garlic is fragrant. Add the stock, vinegar, and crushed tomatoes, scraping up any browned bits from the bottom of the pot. Transfer the brisket back to the Instant Pot.
In a small bowl, mix together the thyme, oregano, garlic powder, paprika and brown sugar. Sprinkle the seasoning over the brisket.
Lock the lid in place and close the venting valve. Select Pressure Cook mode and cook for 1 hour 45 minutes. Allow the pressure to release from the valve on its own for 15 minutes, then manually release the rest of the pressure if necessary.
Add the onions, carrots and potatoes to the Instant Pot. Lock the lid in place and close the venting valve. Select Pressure Cook mode and cook for 15 minutes. Manually release the pressure.
Set the Instant Pot to Sauté mode. Using a slotted spoon, transfer the potatoes and carrots to a serving platter. Transfer the brisket to a cutting board. Bring the sauce to a simmer and cook, stirring, until the liquid is reduced by half, 10-15 minutes.
Carve the brisket, cutting against the grain, into ½-inch thick slices. Arrange on the serving platter with the vegetables. Pour the sauce over everything and serve.
