Your challenge, should you choose to accept it, is to, with a POD after the Congress of Vienna, bring back the Holy Roman Empire. You may achieve this any way you want. For extra difficulty points, pick a POD after the Treaty of Trianon. Again, you may do this any way you want.
Restrictions:
- The HRE must be internationally recognised, and not just in people's beliefs/delusions.
- It must have at least some territory belonging to it.
For extra points, write a short TL about it.