1. Preheat the oven to 220°C/200°C fan.

2. Place the potatoes in a pan filled with water and boil for 10 minutes or until tender. Drain before mashing with a potato masher, adding salt and pepper to taste.

3. Meanwhile, make a white sauce by first melting the butter in a saucepan over a medium heat. Add the flour and stir for about 2 minutes or until a paste forms. Next, slowly add the milk, stirring all the while, until you have a smooth sauce. Continue to stir the sauce for a further 5–10 minutes until it thickens.

4. Add the lemon juice to the sauce, followed by the stock and mustard. Season to taste with salt and pepper and stir in 1 teaspoon of Parmesan. Bring to a simmer and cook for 1 minute before removing from the heat.

5. Place the fish in an ovenproof dish with the sliced fennel. Pour over the white sauce and top with the sweet potato mash. Sprinkle the remaining Parmesan over the top.

6. Place the dish on a baking tray. Transfer to the oven for 40 minutes or until cooked through and golden.

7. Serve with a green vegetable such as spinach, kale or broccoli.

Cook’s Tip: You can replace the semi-skimmed milk with coconut milk to lend a more Southeast Asian flavour to the fish.

•  340 calories per serving  •