I have always called it "double faced binding" I have some drawings here somewhere. If it is the same as you describe then.......when you get to the corner of the quilt, you fold back the binding and draw an line from the stopping point on a 45 degree angle out from the quilt to the center of the binding and then down in a 45 degree to what will be the back side of the binding. Then cut the binding in this shape and then when you fold it back it makes your mitre on the front and the back. Is this the one you are looking for?