Place the mussels in a pot with the shallots, garlic, and white wine. Cover the pot and steam until the mussels open. Discard any mussels that remain closed after the steaming, then remove the cooked mussels and set them aside.
Reduce the remaining liquid in the pot by half over medium high heat. Add the butter, parsley, salt, and pepper. Pour the liquid over the cooked mussels and serve immediately.