Heat the oil in a large, lidded saucepan over a medium heat and fry the shallots for 5-6 mins until softened. Add the garlic and cook for 1 min more before adding the nduja for a few minutes to release its oil. Pour in the wine and cook for 2 mins to allow the alcohol to evaporate, then tip in the tomatoes and chilli flakes, if using, and season well. Bring to a simmer and cook for 10 mins.

Tip in the mussels, then put the lid on the pan and cook for 5 mins until the mussels open. Discard any that remain closed. Ladle into bowls and scatter over the chopped chives. Serve with crusty bread, if you like.