First, the mussels. Ensure all the mussels are tightly closed and not damaged before you begin to cook; any mussels that are damaged or open should be discarded. The preparation can be done in advance. Wash the mussels in a large bowl and under cold running water.
Mussels that float at this stage are not very fresh, so discard them. Remove any barnacles and beards, but don’t scrub the shells as this can end up colouring the cooking juices. Drain.
Finely chop the onion and peeled garlic and grate the cheese.
In a large saucepan over a medium heat, sweat half the onion, the bay leaves and thyme in the butter for one minute. Increase the heat to high, add the mussels, pour in the wine, cover with a lid and cook for three minutes.
Drain in a sieve over a large bowl and discard any mussels that have not opened. Reserve the cooking juices, you will need about 200ml to make the risotto. Once the mussels have cooled, pick the mussels from their shells, leaving a few in their shells for decoration, and put them all aside.
Now, to the risotto… Melt the butter in a large saucepan on a medium heat. Add the remaining onion, cover with a lid and cook for two to three minutes, until the onion is translucent. Add the garlic and stir in the rice. Add the bay leaves, saffron and cayenne pepper and lightly season with salt. Stir and continue to cook on a medium heat for two minutes, until the grains of rice are shiny.
Pour in the wine and let it boil for 30 seconds – bubble, bubble – and stir. Pour in the mussel cooking liquor and the water or fish stock and stir again. Now cook on the gentlest simmer, with just a single bubble breaking the surface. Cover with a lid and leave for 20 minutes, but it mustn’t boil.
Now it’s time for five minutes of some serious and fast stirring. At full speed, stir the risotto. The grains rub against each other, extracting the starch, and this gives the rice its creaminess. Yet every grain remains whole, unbroken. Taste – the rice should have a slight bite.
Add the cheese, butter and parsley to the risotto, along with the cooked peas and spinach, if using, all the cooked mussels and a strong squeeze of lemon. Stir, taste and correct the seasoning just before serving.