My mother browns the rice in a separate pan from the pot she uses to heat the stock. This is just to save time. You could easily brown the rice and onions, and add cold stock and tomatoes to it, bring to a simmer, cover and cook, all in one pot. If you have homemade stock, use it! That's what will take this Spanish rice from good to great. Check the instructions on the rice package for the proportions of liquid to rice. They can range from 1:1 to 2:1. If your rice calls for 2 cups of water for every cup of rice, then for this recipe, use 4 cups of stock for 2 cups of rice.