Heat a large skillet over medium heat and sauté onions, carrots and celery in oil, stirring occasionally until light brown in color. This will take about 10−15 minutes.
While the vegetables are cooking, rinse the brisket under cool water and pat dry with paper towels. Sprinkle both sides with salt and pepper, then place it in a slow cooker, fatty side up. Turn the cooker on the low setting.
Once the onion has started to turn light brown, add the garlic cloves and cook for 3 additional minutes.
Stir in all of the remaining ingredients and bring to a boil for 2−3 minutes. Pour the onion mixture over the top of the brisket, cover with a lid and allow it to cook on low for 8−10 hours.
Once cooked, carefully remove the brisket and transfer to a cutting board. The meat should literally fall apart, so be careful! Scrape off any excess fat from the top of the brisket if desired. Cut the brisket perpendicular to the direction of the fibers, or ‘against the grain’ into ¼"–½" slices. It is very important that you cut the meat in the correct way, or you will end up with stringy meat instead of fall-apart, fork tender slices of meat.
Remove as much fat as possible from the top of the cooking liquid by using a ladle to skim the top—you can also use a defatting cup if you have one.
Remove the bay leaves and transfer the cooking liquid and vegetables to a blender. Do not fill the blender more than ⅓ of the way full—hot liquids expand greatly when puréed and will explode from the top of the lid if you have added too much! (Take our word for it—you’ll need to work in batches, unless you like scrubbing the ceiling!)
Once you have pureed the gravy, taste it for seasoning. If you find it to be salty, you can dilute it with a bit of water.
Carefully place the sliced meat on a serving dish. Pour the gravy over the meat or serve it on the side. Enjoy!
It’s undeniable that brisket is better when made a day in advance—it also makes it easier to pull dinner together!