As expected I found at Arroz Spanish Rice house what I was looking for. Such amazing food (every single dish I ordered was great). The only country in the world I ate a similar paella is Spain. Starters are simply delicious (croquetas, anchovies, boquerones....).
Also have wide range of wines and a professional and friendly Staff. The Spanish cook (Victor), was always available for us and ready to help when ordering.
Obviously it is not a cheap place but what you pay really worths it (by far). My advice is: If you want Spanish food in Bangkok, go to this restaurant, you will not regret it.