Make rub: Combine 1 Tablespoon brown sugar, 1 teaspoons kosher salt, 1 teaspoon paprika, 1 teaspoon garlic powder and 1/2 teaspoon pepper.
Rub: Press the rub into the brisket evenly around the top and sides. Allow to rest for 15 minutes.
Combine: Place the sliced onions in the bottom of your crockpot. Then place the brisket, fat side up on top. Pour 1 cup bbq sauce on top.
Slow cook: Cook on low for 8-9 hours or until fork tender.
Rest: Remove meat and place on a cutting board. Allow meat to rest 5-10 minutes before slicing. Slice thin against the grain. Pour a little sauce from the slow cooker over top or place back inside the slow cooker.
Notes
Glazed top: Preheat oven to 400°F. Spray the brisket with oil and roast in the oven for 15 minutes, or until browned in spots. Remove from the oven and brush generously with sauce from slow cooker. Return to the oven for 5 minutes, then repeat the basting. Roast for another 5–10 minutes, or until the sauce caramelizes beautifully. . Cutting meat: If you cut against the grain, you'll get slices. If you want more of a shredded meat, slice along the grains of the brisket. Storing: Store leftover meat in a covered container 3-5 days in the refrigerator.