Let the mussels soak in fresh water for 15 minutes. Empty the water and do it again. This will encourage the mussels to get rid of any grit and sediment. You'll notice the bottom of the bowl get dirty - that is great news!
Cut the lemons into ¼" slices.
Create two layers of foil about 12x18" and layer the lemons in the center.
Add about 10-12 mussels on top of the lemons. Leave enough room to fold the foil over and create a sealed foil pack.
Fold the foil over and seal the seam by folding it nicely several times. Turn the foil and fold up the sides to create a sealed pouch.
Grill the Mussels
Heat the grill to 450 degrees on direct heat and place the foil pack on the grill grate for about 8-10 minutes.
The mussels are fully cooked when the shells open up completely. You'll need to carefully open a foil pack to check. Discard any with broken shells and the ones that did not open.
Remove the mussels from the grill on to a sheet pan. There will be juices in the foil pack. Keep that and pour it into a serving dish with the mussels.
Make the Dipping Sauce
Add the cast iron pot to the grill and add the ⅓ cup of butter.
When the butter melts, add in the wine and garlic. Stir well.
After a minute, add the chopped parsley. Stir for a minute and remove the Garlic Wine Butter from the grill.
To serve, let your guests pull the meat off of the shells and dip it in the garlic wine butter!
Notes
Keep the grill temperature high. You want the foil packs to create a nice steam to cook the mussels.Don't skip the filtering process. It only takes about 30 minutes, but it lets the mussels remove a lot of the grit from the meat.The citrus flavors from the lemon slices add a fresh flavor to the meat. This complements the garlic wine butter extremely well.Give your guest the foil pack and a ramekin of the melted butter!