Clean the mussels and wash them thoroughly. Discard opened mussels. Peel and halve the onions and cut into strips. Peel and slice the garlic. Peel and wash the carrots.
Clean fennel, wash it. Cut carrots and fennel into slices. Heat the oil in a pot and fry the onions, garlic, carrots and fennel until transparent. Season with salt and pepper. Pour on white wine and 1/2 litre water and bring to the boil.
Add the mussels, cover and cook over a low heat for about 8 minutes. Pour the mussels onto a sieve and collect the stock. Discard unopened mussels. Measure 500 ml mussel stock and mix with cream.
Arrange the mussels with the vegetables and pour the stock over them.