Scrub and debeard mussels under cold running water, discarding any mussels that are cracked.
Melt butter in a large stockpot or Dutch oven over medium heat. Add garlic, shallots, fennel seeds and red pepper flakes, and cook, stirring frequently, until fragrant, about 2 minutes.
Stir in tomato sauce, stirring constantly, until well combined, about 1-2 minutes.
Stir in chicken stock and wine. Bring to a boil; reduce heat and simmer until slightly reduced and flavors have blended, about 5 minutes. Season with salt and pepper, to taste.
Stir in mussels. Cover, with a tight-fitting lid, and cook until the mussels have opened, stirring once, about 5-7 minutes. Discard any unopened mussels.
Remove from heat; stir in heavy cream, basil and parsley; season with salt and pepper, to taste.