Heat the olive oil in a pan and cook the fennel for 10 minutes until caramelised and soft. Stir in the garlic and cook for 1 minute before adding the fennel seeds and ’nduja, and breaking up with the back of a spoon. Pour in the white wine, add the mussels and stir really well. Put on a lid and cook for 5 minutes, shaking the pan until all of the mussels have opened (discard any that stay closed). Stir really well, add the coriander and stir again, then serve with the sourdough.