Place brisket in the slow cooker on top of the onions and carrots, with the fatty side facing up. The cooking liquid should reach just to the bottom of the brisket; if not, add a little water. Cover and cook on Low for 8 hours. Turn the slow cooker off and transfer brisket to a foil-lined sheet pan. Trim some of the fat if desired.
Rub brisket on all sides with bbq seasoning. Heat oil in Instant Pot on Saute function. Place the seasoned brisket into the pot and sear for 3 minutes per side. Remove with tongs and add the four slices of onion to the bottom of the pot. Place the brisket, fat side up on top of the onions. Whisk together the water, apple cider vinegar and ketchup.
Don’t skip the rest period! When the keto brisket is finished cooking, let it sit undisturbed for 30-60 minutes before slicing, carving, or shredding. The dry rub makes the meat ultra flavorful, but if you want to take it a step further, make our homemade keto BBQ sauce to top it off, or use a sugar free store-bought BBQ sauce.
In a small bowl, mix together the salt, black pepper, brown Swerve, garlic powder, onion powder, smoked paprika, and cayenne pepper (optional if you want your brisket to be a little spicy). Completely coat brisket in dry seasoning mix. Place foil over brisket, wrapping the edges to seal, and place in the refrigerator.