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 1 min.
Pour wine into the pan and stir in black pepper. Bring sauce to a boil, stir in mussels, and cover immediately. Let boil for 1 minute.
Stir mussels again, replace cover, and let boil for 2 more minutes. Shells will begin to open. Stir in parsley, half & half and heavy cream, cover pot, and cook until all shells are open, 1 - 3 minutes.
Serve with toasted bread.