Paella a traditional food from Valencia, Spain. I used Jose Andres seafood paella recipe.
When adding the Sofrito you can add 1 Tbsp for 1 1/2 cup of rice or more if you like. The color will be reddish rather than yellowish depending on how much sofritto you use.
I talked with a Spanish friend whom I meet during my travels, and she mentioned that Onions are not used in Spanish paella. It is believed that onions tend to over power the taste of the saffron.