1. Pre-heat oven to 180C fan-forced (200C conventional). 

2. Place potatoes in a saucepan of cold water. Bring to a boil over high heat then reduce to medium-high and cook for 20 minutes or until soft. Drain, peel, then cool and slice into 1cm thick rounds. Set aside.

3. Pour the wine into a large lidded pot over high heat and bring to a simmer. Add mussels, cover, and cook for 3 minutes or until the mussels open, shaking the pot once. Place a colander over a large bowl and drain the mussels, catching the liquid. Pour the juices into a measuring jug. If you don't have 400ml, top up with water. If you have more, keep it all. Set aside.

4. Remove mussels from shells, discarding shells. Prise open any mussels that remain closed using a butter knife (it's a myth that these are off!). Reserve mussels.

5. To make the crumb topping, mix ingredients together in a medium bowl and set aside.

6. Season the fish with salt and pepper and dust with flour, shaking off excess. Heat the oil in a non-stick frypan over medium-high heat and add fish pieces, cooking each side for 45 seconds just to sear the surface. Remove fish to a rack set over a tray, and set aside until required.

7. Use the same pan to make the creamy sauce. Reduce the heat to medium, melt the butter then add eschalot and cook for 3 minutes until softened. Add flour and cook for 1 minute. While stirring, slowly pour in the cream. Once incorporated, stir in mussel stock, using a whisk if needed to remove lumps. Add salt, pepper, bay leaves and nutmeg and stir. Cook for 5 minutes, stirring frequently, until it becomes a thick, creamy sauce. Remove from heat, add parmesan, stirring to melt, then mix in lemon juice and tarragon.

8. To assemble the pie, pour 1 cup of sauce into the base of a 24cm-diameter round pie dish. Place the fish, mussels, potatoes, prawns and peas on top. Pour over remaining sauce and smooth the surface before sprinkling on the crumb topping. Bake 40 minutes, then rest for 5 minutes before serving, sprinkled with chives if desired.

Notes

To clean the mussels, soak them in water for 5 minutes then scrub any loose bits off the shells. Debeard by pulling the tuft hanging out of the shell towards the hinge. Discard any mussels with big chunks missing from their shells, or that are open when raw and will not stay closed when you press them together. Fresh mussels smell of the ocean. You can tell by the smell if a mussel is off (trust me).

Most firm white fish fillets, such as barramundi, ling or flathead, will work well here. Salmon and trout would also be great. Avoid fish that dries out easily when cooked, such as tuna and kingfish, and oily "fishy" fish such as sardines and mackerel.

This recipe features in Nagi's four days of Easter feasting menu