Hanger steak is actually two muscles joined in the center with a thin strip of connective tissue. Most butchers will split it in half and remove the gristle, but if yours came whole, you will want to cut it in half along one side of the connective tissue and then trim it off the other side. If it came untrimmed, it might also have some silverskin attached (a whitish film on the outside of the meat), which you will want to shave off with a sharp knife.