Put a large pan over a medium heat and melt the butter. Add the shallots with a pinch of salt and cook gently until completely soft. Add the garlic and cook for a minute until fragrant.

Add the mussels and white wine, cover with a lid and cook for 2–3 minutes until the mussels open. Lift them out, discard any that haven’t opened, keeping the cooking liquor in the pan.

Once cool enough to handle, remove the mussels from their shells and discard the shells.

Put the pan back on a medium heat, add the cream and bring to a gentle simmer. Whisk in the corn flour slurry until the sauce thickens enough to coat the back of a spoon, then take it off the heat and stir through the parsley.

Gently fold in the peas to cool the mixture down, then add the diced white fish, trout and the mussels. Season lightly, then transfer to a baking dish.

Pipe on mash potato, top with breadcrumbs laced with grated cheddar and bake at 200°C for 20–25 minutes until golden and crisp and bubbling at the edges. Rest briefly before serving.