Rinse the mussels well under cold water. Pick them over, pulling off any beards and discarding any mussels that are broken or gaping open. In a large pot with a lid, heat the oil and butter over medium heat. Add the garlic, shallots, and red pepper flakes and cook until fragrant and soft but not colored, 3 to 5 minutes.
Add the mussels, wine, and half of the parsley. Increase the heat to high, and cover the pan. After 2 minutes, remove the lid and toss the mussels well with a large spoon. Cover the pot again and cook until the mussels have opened wide, another 3 to 4 minutes. Add the remaining parsley, give the mussels a final toss, and divide the mussels and the broth among bowls & serve immediately.