Heat olive oil in a saucepan and sweat the chopped onion until translucent. Add the rice and sweat with it. Add the saffron, salt, pepper and tomato paste, fry briefly and then deglaze with a dash of sherry. Add the chicken stock and bring to the boil. Then leave the lid on for 10 minutes over the lowest heat until the rice has absorbed the stock.
Goes well with grilled tuna or scampi fried with garlic.