public class Key extends Sprite
{
    private var letter:String;
    public static const CLICKED:String = "clicked";

    private function keyClicked(e:MouseEvent):void {
        this.removeEventListener(MouseEvent.CLICK, keyClicked, false);
        this.mouseEnabled = false;
        dispatchEvent(new Event(CLICKED));
    }
}

addEventListener(Key.CLICKED, keyboardGuess);

public function keyboardGuess(e:Event):void {
        trace("event received");
        var letter:String = e.target.getLetter();
        trace(letter);
    } //there will be other functionality in here when I get it listening

dispatchEvent(new Event(CLICKED, true));