Preheat oven to 500°.
Place mussels in a large bowl; cover with cold water. Sprinkle with cornmeal; let stand 30 minutes. Drain; rinse mussels.
Place rock salt in bottom of a shallow roasting pan. Arrange mussels in a single layer on rock salt. Bake at 500° for 5 minutes or until shells open. Remove mussels from pan; set aside, and keep warm. Discard rock salt and any unopened shells.
Combine wine, vinegar, shallots, and pepper in a small saucepan. Cook over medium heat 5 minutes or until thoroughly heated. Serve with mussels.