FOR THE MASH
3lbs large potatoes, peeled and diced into 1 inch squares
½ cup milk, warmed
kosher salt and freshly ground black pepper
FOR THE BASE
1 tablespoon vegetable oil
1 yellow onion, very finely chopped
8oz chestnut mushrooms, thickly sliced
3 large handfuls fresh spinach
¾ cup milk
¾ cup heavy cream
⅓ cup all-purpose flour
2oz unsalted butter
4½oz strong Cheddar, grated
2 teaspoons Taste #5 Umami Bomb
½ teaspoon mustard powder
juice of half a lemon
1 tablespoon chopped fresh flat-leaf parsley
½lb cod or haddock fillet, chopped into large chunks
1 cup medium peeled cooked prawns (shrimp)
1 cup frozen peas
Kosher salt and freshly ground black pepper
- Preheat oven to 400°F.
- Meanwhile, cook the potatoes in salted, boiling water for about 10 minutes, or until tender. Drain, then return to the pan.
- Add the butter, then while beginning to mash gradually add the warm milk (you may not need all of it). Season to taste.
- Heat the oil in a medium saucepan, and fry the onion and mushrooms for 4-5 minutes, or until soft. Add the spinach and cook for a further 2 minutes, until it has wilted and some of the water has evaporated.
- In a separate pan, place the milk, cream, flour and butter together and gradually bring to simmering point, whisking continuously, until the sauce becomes thick and smooth. Reduce the heat to low, and allow the sauce to cook very gently for 5 minutes, stirring occasionally.
- Remove from the heat and stir in the cheese, ensuring it is thoroughly melted through the sauce. Stir in the Umami Bomb, nutmeg, mustard powder, lemon juice and parsley. Season with salt and freshly ground black pepper. The sauce will appear rather thick, but will thin out in the oven once baked.
- Place the cooked vegetables, fish, prawns and peas into an appropriately sized earthenware dish. Pour over the white sauce and then top with the mashed potato (for extra deliciousness, a sprinkling of Parmesan cheese can be added on top the mashed potato).
- Place in the oven for 25-30 minutes, until piping hot and golden brown. Leave to stand for five minutes before serving.