Mussels need to be cleaned, rinsed several times and have any traces of beard removed. Most prepared Mussels will be prepared for you just to rinse with perhaps a little beard to remove, but with wild Mussels you need to take a little more care.
Tap the shells of any Mussels whose shells are open when you are clearning. If there are any Mussels with open or broken shells left, remove them and bin. I only had to discard 3 Mussels out of my bag. Mussels must be cooked live, so they need to be fresh.
Use a large pan, add the olive oil, butter, shallots and garlic. Shallow cook until the shallots are soft and then add the water, sherry, parsley, lemon juice and a touch of salt and pepper. Simmer for a minute while stirring.
Add the live Mussels to the pot and steam them for 5 - 10 minutes. Mussels don't take long to cook. Shake the pan a couple of times while cooking to move the broth and the Mussels around. When the shells open, the Mussels are ready.
Remove any unopened Mussels and serve them in a dish with their broth and some bread.