For the Mussels:
1 tablespoon (15ml) extra-virgin olive oil
2 large shallots (3 ounces; 85g), thinly sliced
2 garlic cloves (10g), thinly sliced
2 ounces (1/4 cup; 60g) ‘nduja (see note)
1 cup (240ml) dry white wine
2 pounds (900g) mussels, scrubbed and debearded (see note)
1/4 cup (15g) chopped fresh flat-leaf parsley leaves
1 tablespoon (15ml) lemon juice and 1 teaspoon (2g) finely grated zest from one lemon
1 loaf rustic sourdough bread, thickly sliced, drizzled with olive oil, and broiled until heavily toasted
In a large saucepan, heat oil over medium heat until shimmering. Add shallots and garlic, season lightly with salt, and cook, stirring frequently, until softened but not brown, 5 to 7 minutes.
Add ‘nduja and, using a wooden spoon, break it into pieces and stir vigorously to combine with shallots and garlic. Continue to cook, stirring frequently, until fat from ‘nduja separates and shallots and garlic are stained red and fully coated with ‘nduja, 3 to 5 minutes longer. Add wine, increase heat to high and bring to a boil.
Add mussels, stir, cover, and cook, shaking pan constantly and peeking every 30 seconds to stir. Cook just until all the mussels are open, 2 to 4 minutes. Remove from heat, and using tongs, quickly transfer mussels to a warmed heatproof serving bowl. Cover mussels with saucepan lid to keep warm. Add parsley, lemon juice, and zest to saucepan and stir to combine. Taste the liquid, and adjust seasoning with salt if needed.
For Serving: Remove lid from the serving bowl, and pour contents of saucepan over mussels. Serve immediately, passing toasted bread at the table along with a large empty bowl for collecting spent mussel shells.