1

Cook the cauliflower in a large pan of boiling water for 8-10 minutes, or until completely tender. Drain and set aside in a colander for a few minutes to steam-dry. Transfer to a food processor with the crème fraîche and blitz to a purée. Season and set aside.

2

To make a white sauce, heat the butter in a frying pan over a medium heat until frothy. Add the flour and stir well to make a paste. Cook over a low heat for 2 minutes, then gradually add the milk, stirring well between each addition, until you have a smooth sauce. Simmer gently for a few minutes, until the sauce thickens. Add the mustard, and season well.

3

Preheat the oven to 200°C, fan 180°C, gas mark 6. Wilt the spinach briefly in the microwave, then squeeze out as much water as possible and add to the sauce, along with the fish. Transfer to a 20cm x 26cm pie dish.

4

Top with the cauliflower mash, either piping it on in swirls using a piping bag fitted with a star nozzle, or forking over the surface to create a rough texture. Scatter over the parmesan and bake for 20-25 minutes, then finish it off under a hot grill for 5 minutes to get a crisp, golden crust.

5

Serve with green vegetables on the side.