Preheat oven to 600°F, position rack in the center position and place cast iron skillet in the oven.

Wash, debeard and dry the mussels, discarding any broken ones or ones that do not close when tapped on the shell.

Washing and Debearding Mussels: run the mussels under cold water and brush off any barnacles or debris that could be on the shell. Discard any broken mussels. If any are open, lightly tap the shell - if it closes, it's alive; if it doesn't close, discard it. The "beard" is a clump of fibers that sprout from the shell. While farm-raised are fairly clean, if you see any with a beard, grab it with a pairing knife and your finger, and give it a good tug it toward the hinge of the shell. It should come right off.

Place dry mussels in a bowl and coat with extra virgin olive oil, about 1-2 Tablespoons. Generously sprinkle with sea salt. Set aside.

While the oven is coming to temperature, spread compound butter on ciabatta bread slices and toast on a skillet until golden brown.

Ten minutes after the oven has reached 600°F, transfer the mussels onto the cast iron skillet. They should immediately sizzle and smoke. Close the oven door and roast the mussels for about 1 ½ minutes.

Remove from the oven, serve with ciabatta bread and melted butter. Enjoy!