BBC Food - Recipes - Halibut with crab and lime croquettes

Ingredients

• rock salt , to cover base of a baking tray
• 3 large Maris Piper potatoes
• 100g/3½oz picked crab , white and brown meat
• 2 lime , zest only
• 100g/3½oz plain flour
• ready-made breadcrumbs
• 2 free-range eggs , beaten
• vegetable oil , for deep fat frying
• 6 carrots
• 200g/7oz chestnut mushrooms , chopped into quarters
• knob of butter
• 300g/10½oz baby spinach
• 1 litre/1¾ pint fresh fish stock
• 250g/9oz butter
• 50ml/2fl oz vermouth
• salt and freshly ground black pepper
• dash vegetable oil
• 6 pieces of halibut , skin on