2 tbsp vegetable oil
2 large onions, thinly sliced
150g tomato paste
2 tsp ground paprika
1 tsp dried oregano
2 tsp onion powder
1 tsp kosher salt, plus more for the meat
1/2 tsp ground cumin
1/2 tsp ground cinnamon
1/2 tsp freshly ground black pepper, plus more for the meat
250ml beef stock
250ml apple cider vinegar
100g light brown sugar
1.5kg beef brisket (preferably flat cut)
Heat the oil in a large frying pan over medium-high heat. Add the onions and cook, stirring occasionally, until softened and beginning to brown and char in some spots, about 8 minutes.
Add the tomato paste, paprika, oregano, onion powder, salt, cumin, cinnamon and cook until fragrant, about 2 minutes more. Deglaze the pan with stock, using a wooden spoon to scrape the browned bits from the bottom of the pan. Add the vinegar and sugar and stir to combine and dissolve the sugar. Bring to a boil. Reduce the heat to low and simmer for 10 minutes. Transfer to slow cooker.
Pat the brisket dry with paper towels. Generously season both sides with salt and pepper. Place the brisket in the slow cooker fat-side down.
Cover and cook on the LOW setting for 6 to 8 hours. The brisket is done when it easily shreds when pulled, but it shouldn’t be falling apart.
Transfer the brisket to a clean cutting board. If desired, use a spoon to scrape the fat cap off. Now you can slice and serve the brisket immediately with the sauce.