Trim excess fat from brisket. Season meat with a little salt and pepper. Place in a 13x9x2-inch baking pan; cover with onion slices. Sprinkle lightly with salt. Reserve 1/3 cup beer. Combine remaining beer and next 6 ingredients; pour over meat. Cover with foil.
Bake in a 350 degree oven for 3 to 3 1/2 hours or till tender. Remove meat to a platter; keep warm. Skim off excess fat from pan juices; remove bay leaf.
In a saucepan cook juices down to 2 cups. Combine reserved beer and flour; stir into pan juices. Cook and stir until thickened and bubbly. Cook and stir 1 to 2 minutes more. Season with salt and pepper to taste.
Slice meat across the grain; pass gravy. Serves 6 to 8.