Defrost the mussels if using frozen. Heat a splash of oil in a large saucepan over a medium-high heat and add the lardons. Cook for around 4-5 mins, then add the cumin and mustard seeds. Once the mustard seeds start to spit, add the garlic, leek and carrots. Season with sea salt and stir well. Cook for 10-12 mins, over a medium-low heat, until the leek starts to soften, mix in the chilli flakes and curry powder. Continue to cook for 1-2 mins until fragrant, then splash in the wine. Reduce over a high heat until the wine has almost completely evaporated, around 2-3 mins.

Mix in the flour then stir in the potatoes, fish stock and double cream. Leave everything to gently bubble away for 15 mins, over a medium-low heat, stirring often. Once the sauce starts to thicken, stir in the fish pie mix and the mussels, including their sauce. Pop a lid on and leave it to bubble away on a medium heat for about 4-5 mins. If the mussels are fresh, discard any that don't open. Finish with a sprinkle of chopped coriander and parsley and a big squeeze of lemon. Serve with fresh crusty bread, if you like.