Place brisket in a large roasting pan. Pour beer over the meat then place onion sections on top. Season with garlic, salt and pepper. Combine the BBQ sauce, molasses and liquid smoke; pour over the roast. Cover pan with aluminium foil.
Place pan on the centre rack of the preheated oven and bake for 6 to 8 hours or until beef is fork tender. Remove from the oven and let stand for about 10 minutes before slicing across the grain into thin slices.
Leftovers make excellent sandwiches for Shabbat.
To keep it kosher, make sure all your prepared ingredients are kosher.