3/4 cup BBQ sauce of choice,plus more for serving (optional)
1tablespoonchopped fresh parsleyfor garnish
Season the brisket with 1 1/2 teaspoons salt, paprika, garlic powder, and pepper to taste.
Heat 2 teaspoons oil in a large cast iron or heavy skillet over medium-high heat. Add the brisket and cook until browned on both sides, about 5 minutes per side. Transfer to a 5 to 6 quart slow cooker (an oval cooker is ideal). Pour the liquid smoke over the brisket.
Heat the skillet over medium-low heat. Add the remaining 1 teaspoon of oil and the onions and cook, stirring constantly, until soft and golden, about 15 minutes. Place onions on top of the brisket in the slow cooker and sprinkle with 1/4 teaspoon salt and more pepper to taste. Pour the BBQ sauce on top. Cover and cook on low for about 8 hours, until tender.
Remove the brisket and transfer to the cutting board. Using a sharp knife, slice the meat across the grain into approximately 1/2 inch thick slices. Place the sliced meat back into the slow cooker, arranging the meat like fallen dominoes and submerging it into the liquid and onions. Cook for about 1 hour more, until very tender. Keep warm until ready to serve.
Top with the fresh parsley just before serving. Serve with more BBQ sauce (if using). (To freeze, store cooked brisket and sauce in an airtight container.
REFRIGERATE AND SERVE LATER:
To prep the night ahead, follow all the steps up to turning on the slow cooker. Refrigerate, covered until ready to cook. In the morning, remove from the refrigerator. cook on low for about 8 hours 30 minutes before continuing with the recipe (the extra 30 minutes accounts for stating with a cold ceramic). Note: Never place your stoneware (whether it has been refrigerated or is at room temperature) in a preheated slow cooker.