What is the ingredient that makes a Spanish paella so particular? I have eaten paella in Spain; I then ate it in Italy, but it didn't taste like the one in Spain.

What is the ingredient that makes the Spanish paella so particular?
I remember they used a particular sauce for the meat (I have eaten both the Valencian paella and the seafood paella); if that is what makes the difference, what are the ingredients for that sauce?
The most prominent flavors in authentic paella are pimenton (smoked paprika), saffron, a sofrito of onion and tomato, garlic, and the broth.