To make the halibut, preheat the oven to 200C/180C Fan/Gas 6.
Place 10g/⅓oz of the butter into a saucepan over a medium-low heat then add the shallot and garlic. Sweat for 10 minutes until soft, then transfer to a bowl and allow to cool.
Add the prawns to a food processor and blend to a paste. Transfer to a bowl and stir through the chives, cornflour and cooled shallots. Season with salt and pepper.
Spread this mixture generously on top of the halibut fillet. Place this in a pan with the stock and remaining 25g/1oz butter, cover with a damp cartouche and bake for 10 minutes. Remove the fish and keep warm.
To make the sauce, heat the fish stock in a saucepan and allow to reduce by half. Add the cream and bring back to the boil. Add the freshly cracked pepper and dill. Season with a pinch of salt and add some lemon juice.
Sprinkle the halibut with the toasted breadcrumbs just before serving. Serve the sauce with the fish and wilted spinach.
