- Melt butter in a large stock pot over medium heat. Add garlic and let sizzle for about 30 seconds. Season with red pepper flakes and lemon zest, stirring for about 45 seconds.
- Quickly pour in wine into the pan and season with black pepper. Bring sauce to a boil, stir in mussels, and cover immediately. Shake pot and let boil for 1 minute.
- Stir mussels, replace cover, and let boil for 2 more minutes. The shells will begin to open. Stir in parsley, cover pot, and cook until all shells are open, 1 to 3 minutes.
- Serve with grilled bread and lemon wedge.