In a small saucer, stir together the lemon juice and the saffron and leave to soak for 15 minutes.

In a large saucepan, heat the olive oil over medium heat.

Add the onion and saute for 4 to 5 minutes, or until softened.

Add the garlic and stir for 1 minute more, until the aroma of the garlic is released.

Add the rice and stir for 3 to 4 minutes, until the kernels are slightly toasty and make a clicking noise on the pan.

Stir in the lemon juice and saffron mixture, then add the chicken stock and bring to a boil.

Add the fresh peas, if using, otherwise add the frozen peas during the last 10 minutes of cooking time.

Reduce the heat so that the liquid is simmering.

Cover and simmer for 20 to 25 minutes, stirring occasionally, until the liquid is absorbed and the rice is tender.

Serve hot.