Add butter and when melted, add chopped onion, paprika, red pepper flakes and freshly ground black pepper. Cook, stirring, until onions are tender, about 4 minutes. Add the garlic and tomatoes, and cook, stirring, for 2 minutes.
Add the wine, heavy cream and parsley. Stir in sausage. Add mussels and bring to a boil. Lower heat and cover, cooking until the mussel shells have opened, about 6-8 minutes.
With a ladle, serve mussels with sausage and sauce into bowls. Discard any shells that have not opened.