Instructions

1. Preheat the oven to 190 degrees celsius
2. In a pan, steam the spinach until it's wilted and set aside
3. Prepare the mashed potato topping by peeling the potatoes and boiling them on a medium heat until the potatoes can be easily broken by a fork
4. Drain the boiled potatoes, then pop them back in the pan, add a splash of milk and half the butter, season well, then mash until smooth and lump free
5. To make the roux, melt the butter in a pan. Add the flour and mix together with a whisk until a thick paste forms
6. On a low heat, whisk in the rest of the milk until the paste and milk are combined and season well. Stir occasionally until the sauce has thickened slightly
7. Add in the fish bone broth, the mustard, a squeeze of lemon and the bay leaves and stir until combined. Leave to simmer very gently for a few minutes until thickened slightly
8. Once thickened slightly, add in 50g of the cheddar and stir until incorporated
9. In a oven proof dish, add the fish and wilted spinach in an even layer over the bottom of the dish
10. Pour over the white sauce onto the fish and spinach, ensuring it is distributed evenly
11. Add the mashed potato as a top layer to the dish. Sprinkle over the remaining cheddar on top
12. Place the dish in the oven for 25-30 minutes until the top is golden brown and the sauce is bubbling
13. Leave to cool for 15 minutes before serving