The highest award was the Grand Cross to the Iron Cross, awarded only once to Hermann Goring, The cross you asked about was the Knights Cross to the Iron Cross with gold oak leaves, swords, and diamonds, awarded only once to Luftwaffe Stuka pilot Hans- Ulrich Rudel. The highest scoring Luftwaffe ace was Erich Hartmann, who recieved the Knights Cross to the Iron Cross silver Oak Leaves, swords, and diamonds.
http://www.angelfire.com/nj/ww2/grandcross.html