How to Make It
In a large skillet, cook the sausage over moderately high heat, breaking it up with a spoon until crisp, about 15 minutes. Transfer to a plate.
Wipe out the skillet, add the olive oil and heat until shimmering. Add the onion and cook over moderately high heat until translucent, about 3 minutes. Add the red pepper and fennel and cook over low heat until just tender, about 15 minutes.
Add the garlic, tomato sauce and clam juice and season with salt and pepper. Bring to a simmer, then add the mussels and the reserved sausage. Cover and cook over moderately high heat until the mussels open, about 10 minutes. Discard any unopened mussels. Season with salt and pepper, garnish with the dill and serve at once with grilled bread.