Quantities are very much a personal choice. I usually allow 2kg of Mussels for 2 people!

You will need:

2kg of Fresh Mussels. Shells scrubbed, de-bearded, and well drained
1 tablespoon of Extra Virgin Olive Oil
1 Leek, washed, sliced and diced
1 teaspoon of Fennel Seeds
150ml of White Wine (you can use more)
150ml of thick Natural Yoghurt (you can use more)
2 tablespoons of chopped parsley.
Black Pepper

Optional flavourings can also be fresh chilli or garlic added when you cook the leek

Heat a large pot over a high heat and then toss in all the (drained) mussels.
Give the pot a good stir with a wooden spoon then pop the lid on for a couple of minutes. Check how the mussels are cooking, stir again and pop the lid back on for another minute or so, by which time they should be opened.
With a slotted spoon remove mussels to a large bowl or serving dish.
Cover with cloth and put aside will you quickly make the sauce for the mussels.

Drain and rinse the pot of any liquid from cooking the mussels (this will get rid of any gritty bits). If you wish to fine strain the cooking liquid some of this can be added to the final sauce

Put the pot back on a moderate heat with about 1 tablespoon of Olive oil in the pan. Sweat off the leek and fennel seeds for 2 to 3 minutes until translucent.
If using chilli, garlic add at this stage.

Once the leek is softened add the white wine and continue to stir and reduce the sauce slightly. Only a couple of minutes and then finally add the yoghurt and parsley, stir well to incorporate into the sauce and then to prevent curdling immediately take off heat and pour the leek and sauce all over the mussels.

Serve garnished with parsley leaves!