Place the half shell mussels in a pot, cover with water, season with salt and bring to a boil. Cook for 2 minutes then turn down the heat and remove the mussels from the pot, retaining the water.
Add the saffron to a small cup and cover with boiling water. Set aside to steep.
Heat a pan over medium-high heat, add the olive oil then fry the onion, spring onion and celery for a minute or two. Add the garlic and the rice an fry for another minute or two.
Add the saffron and the water retained from cooking the mussels. Season with salt and black pepper, cover and cook over medium heat for around 15 minutes, or until the rice is almost cooked.
Add the fresh herbs, then add the half shell mussels as well as the uncooked mussel meat to the pot. Cover and cook for another 5 minutes.
Remove the pot from the heat, add a squeeze of lemon juice and transfer to a serving dish. Garnish with parsley and serve with some extra lemon wedges.
