1. Thaw frozen mussels overnight in the refrigerator. They will open once you break the packaging seal. Remove half of the shells.
2. In a saucepan, combine butter, salt and garlic over low heat until the butter is melted and the garlic is soft.
3. Using a teaspoon, top each mussel with melted butter and garlic. Add grated cheese on top.
4. Arrange mussels on a baking tray lined with aluminum foil and bake for 10-15 minutes at 180°C (355°F).
5. Remove once cheese has browned. Serve and enjoy!