Preheat a medium-high grill. Cover the grill rack with foil and arrange the halibut fillets on top – or place them on a greased baking sheet. Sprinkle with the juice from half the lemon. Season with salt and pepper, and share half the butter between them. Grill for 6 to 8 minutes, turning once.
Meanwhile, heat the remaining butter with the olive oil in a large frying pan. Add the fennel and cook it for 2 or 3 minutes, until softened and beginning to brown.
Tip the cannellini beans into the pan with the fennel. Add the lemon rind and remaining lemon juice with the stock powder or cube and a splash of hot water. Cook over a medium-high heat, stirring occasionally, for 4 or 5 minutes.
Share the bean mixture between four warmed plates or shallow bowls. Arrange the halibut fillets on top, then scatter the capers and parsley over them. Serve immediately.
Cook’s tip: You could add a couple of skinned, chopped tomatoes and a handful of baby spinach to the cannellini beans – just add them 2 or 3 minutes before the end of cooking time, so that the spinach wilts.
• 4 x 150g (6oz) fillets wild Alaska halibut
• Finely grated rind and juice of 1 lemon
• Salt and freshly ground black pepper
• 25g (1oz) butter
• 1 tbsp olive oil
• 1 bulb fennel, finely sliced
• 2 x 400g cans cannellini beans, drained and rinsed
• 1 tsp vegetable stock powder or ½ vegetable stock cube
• 2 tbsp capers
• 2 tbsp roughly chopped flat leaf parsley, roughly chopped