Place a large saucepan on the heat, add 100ml water and the cleaned mussels and cover with a lid. Bring to the boil and steam the mussels for 4–5 minutes. Once the mussels have opened, drain through a sieve covered with muslin (for catching any grit), or a very fine sieve, but retain their juices. Discard any that have not opened and remove all the mussel meat from the rest of the shells, keeping 8 intact for garnishing. Set the meat aside in a small bowl and discard the shells.
Heat a large sauté pan and put in the butter. Once it has melted, add the shallots and cook over a medium heat for 4 minutes until they are soft but not coloured, then add the rice. Coat the rice in the butter and shallots and turn up the heat. Add the white wine and the reserved juices from the mussels and let the liquid reduce by a third.
Start to add the hot stock to the rice, a ladleful at a time, and continue stirring. Once the moisture has been absorbed and the mixture starts to look creamy, add another ladleful of stock. Continue to cook for 10 to 15 minutes, adding the stock gradually, until the rice grains are al dente and the risotto has a loose consistency that would drop off a spoon easily.
Stir in the cooked mussels and the cold cubed butter and warm through.
Spoon the risotto into the centre of 4 serving plates and garnish with the dill, chervil and 2 mussels in their shells on each risotto. Finish with a drizzle of rapeseed oil.